AU2021106825A4 - Method for exploring skarn-hydrothermal vein iron polymetallic ore in plateau desert area - Google Patents
Method for exploring skarn-hydrothermal vein iron polymetallic ore in plateau desert area Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V20/00—Geomodelling in general
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/40—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for measuring magnetic field characteristics of the earth
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/24—Earth materials
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- Engineering & Computer Science (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- Geophysics And Detection Of Objects (AREA)
Abstract
The present disclosure provides a method for exploring a skarn-hydrothermal vein iron
polymetallic ore in a plateau desert area, including: determining a type of a metallogenic system,
and delineating a favorable mineralization zone of a magmatic ore deposit; carrying out a
gravimetric survey on the magmatic zone and a geological anomaly area to delineate a gravity
gradient belt; carrying out a high-accuracy magnetic survey on the gravity gradient belt or the
geological anomaly area to delineate a magnetic anomaly; carrying out electromagnetic profiling on
the anomaly area or the delineated magnetic anomaly to decompose the anomaly and narrow a
target, and determining an anomaly distribution feature and a spatial position for positioning a
magnetic body; and verifying, with a deep drilling technology, the anomaly distribution feature and
the spatial position for positioning the magnetic body, and exploring a change of a skarn iron
polymetallic ore in grade, thickness, scale and occurrence. The exploration method combined with
the "metallogenic system+high-accuracy magnetic survey+gravimetric survey+electromagnetic
profiling inversion+WFEM+drilling" in the present disclosure can distinguish the skarn iron
polymetallic ore and the hydrothermal vein polymetallic ore more effectively.
19
- 1/4
101
Determine a type of a metallogenic system according to a spatio-temporal
feature and a regional geological background in mineralization of a magmatic
ore deposit and ore spot, and delineate a favorable mineralization zone of the
magmatic ore deposit
102
Carry out a 1:50,000 gravimetric survey on the favorable mineralization zone
of the magmatic ore deposit, to delineate a gravity gradient belt
103
Carry out a 1:50,000 high-accuracy magnetic survey on the gravity gradient
belt according to a historical aeromagnetic anomaly inspection condition in
the magmatic zone, to delineate a magnetic anomaly
104
Carry out 1:2,000 electromagnetic profiling on the favorable mineralization
zone of the magmatic ore deposit or the delineated magnetic anomaly to
decompose the anomaly and narrow a target, and determine an anomaly
distribution feature and a spatial position for positioning a magnetic body
105
Verify, with a deep drilling technology, the anomaly distribution feature and
the spatial position for positioning the magnetic body, and explore a change
of a skarn iron polymetallic ore in grade, thickness, scale and occurrence
106
Carry out a WFEM on a non-magnetic anomaly area between M1-M3
magnetic anomalies and the gravity gradient belt to separate a distribution
range and a buried depth of each of a stratum and a rock mass
Verify the distribution range and the buried depth of each of the stratum and 107
the rock mass with the deep drilling technology, and explore a change of a
hydrothermal vein polymetallic ore in grade, thickness, scale and occurrence
FIG. 1
Description
- 1/4
101 Determine a type of a metallogenic system according to a spatio-temporal feature and a regional geological background in mineralization of a magmatic ore deposit and ore spot, and delineate a favorable mineralization zone of the magmatic ore deposit
102 Carry out a 1:50,000 gravimetric survey on the favorable mineralization zone of the magmatic ore deposit, to delineate a gravity gradient belt
103 Carry out a 1:50,000 high-accuracy magnetic survey on the gravity gradient belt according to a historical aeromagnetic anomaly inspection condition in the magmatic zone, to delineate a magnetic anomaly
104 Carry out 1:2,000 electromagnetic profiling on the favorable mineralization zone of the magmatic ore deposit or the delineated magnetic anomaly to decompose the anomaly and narrow a target, and determine an anomaly distribution feature and a spatial position for positioning a magnetic body
105 Verify, with a deep drilling technology, the anomaly distribution feature and the spatial position for positioning the magnetic body, and explore a change of a skarn iron polymetallic ore in grade, thickness, scale and occurrence
106 Carry out a WFEM on a non-magnetic anomaly area between M1-M3 magnetic anomalies and the gravity gradient belt to separate a distribution range and a buried depth of each of a stratum and a rock mass
Verify the distribution range and the buried depth of each of the stratum and 107 the rock mass with the deep drilling technology, and explore a change of a hydrothermal vein polymetallic ore in grade, thickness, scale and occurrence
FIG. 1
[01] The present disclosure relates to the technical field of solid ore prospecting, and in particular, to a method for exploring a skam-hydrothermal vein iron polymetallic ore in a plateau desert area.
[02] The prospecting method is the collective name of working methods and technical measures taken for the sake of finding ore resources. The prospecting is the geological work carried out in certain areas to find and evaluate ores for the national economy. With the comprehensive utilization of effective technical means and prospecting methods, it prospects the ores in favorable zones, and evaluates and researches the found ore spots or ore deposits, thereby providing necessary ore resource data as well as geological, technical and economic data to further select deposit exploratory areas (or zones or exploration areas) and formulate the far-seeing development plan for the national economy.
[03] The desert area in the south of the Qinghai Qaidam paraplatform of the Qinghai-Tibet Plateau is affiliated to the Early Palaezoic aulacogen in the Qimantag area of the East Kunlun Mountain in Qinghai Province. In deposits of skarn-hydrothermal vein iron polymetallic ores, ore-forming mother rocks are intermediate-acidic intrusive rocks mainly, and surrounding rocks are carbonate rocks in the Cambrian-Ordovician Tanjianshan Group and upper carboniferous Di'aosu formation. Orebodies are mostly distributed in outer contact zones and comprehensively controlled by the intrusive contact zones, magmatite conditions, lithology of the surrounding rocks, faults, fractures and interlayer structures.
[04] Skam-hydrothermal vein iron polymetallic ore deposits and spots in the plateau desert area are different from other areas in natural landscape. Due to the large coverages of quaternary wind-drift sand and little rock outcrops in the desert area, the conventional large-scale geological mapping and geochemical prospecting survey cannot be carried out, the prospecting effect is undesirable and the prospecting efficiency is low.
[05] An objective of the present disclosure is to provide a method for exploring a skam-hydrothermal vein iron polymetallic ore in a plateau desert area, to solve the problem that ores cannot be accurately prospected under landscape restrictions and complex landforms in the plateau desert area.
[06] To implement the above objective, the present disclosure provides the following solutions:
[07] A method for exploring a skam-hydrothermal vein iron polymetallic ore in a plateau desert area includes: determining a type of a metallogenic system according to a spatio-temporal feature and a regional geological background in mineralization of a magmatic ore deposit and ore spot, and delineating a favorable mineralization zone of the magmatic ore deposit;
[08] carrying out a 1:50,000 gravimetric survey on the favorable mineralization zone of the magmatic ore deposit, to delineate a gravity gradient belt;
[09] carrying out a 1:50,000 high-accuracy magnetic survey on the gravity gradient belt according to a historical aeromagnetic anomaly inspection condition in the magmatic zone, to delineate a magnetic anomaly;
[10] carrying out 1:2,000 electromagnetic profiling on the favorable mineralization zone of the magmatic ore deposit or the delineated magnetic anomaly to decompose the anomaly and narrow a target, and determining an anomaly distribution feature and a spatial position for positioning a magnetic body;
[11] verifying, with a deep drilling technology, the anomaly distribution feature and the spatial position for positioning the magnetic body, and exploring a change of a skarn iron polymetallic ore in grade, thickness, scale and occurrence;
[12] carrying out a wide-field electromagnetic method (WFEM) on a non-magnetic anomaly area between M1-M3 magnetic anomalies and the gravity gradient belt to separate a distribution range and a buried depth of each of a stratum and a rock mass; and
[13] verifying the distribution range and the buried depth of each of the stratum and the rock mass with the deep drilling technology, and exploring a change of a hydrothermal vein polymetallic ore in grade, thickness, scale and occurrence.
[14] Optionally, the metallogenic system may be a magmatic iron polymetallic ore system.
[15] Optionally, the delineating a magnetic anomaly may specifically include: carrying out positioning and the magnetic survey according to a theoretical coordinate by using a regular grid of 500*100 m, a high-accuracy proton magnetometer and navigation and positioning functions of a handheld global positioning system (GPS) during the high-accuracy magnetic survey, and delineating the magnetic anomaly according to surveyed data.
[16] Optionally, the gravimetric survey may be implemented by using a grid of 500*100 m and a high-accuracy CG-5 gravimeter, acquiring field gravimetric observation data with a precise point positioning (PPP) technology, and delineating the gravity gradient belt according to the gravimetric observation data.
[17] Optionally, the 1:2,000 electromagnetic profiling may be implemented by arranging a profile in perpendicular to a long-axis direction of the delineated magnetic anomaly, carrying out the high-accuracy magnetic survey at a point distance of 5 m with a real-time kinematic (RTK) positioning technology, carrying out an inversion with geochemical inversion software and positioning the spatial position of the magnetic body.
[18] Based on specific embodiments provided in the present disclosure, the present disclosure discloses the following technical effects:
[19] According to regional geological features, ore-bearing formations, mineralized zones and ore-controlling factors of the iron polymetallic ore deposits, the exploration method combined with the "metallogenic system+gravimetric survey+high-accuracy magnetic survey+electromagnetic profiling inversion+WFEM+drilling" in the present disclosure can distinguish the skarn iron polymetallic ore and the hydrothermal vein polymetallic ore more effectively.
[20] To describe the technical solutions in the embodiments of the present disclosure or in the prior art more clearly, the accompanying drawings required for the embodiments are briefly described below. Apparently, the accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art may still derive other accompanying drawings from these accompanying drawings without creative efforts.
[21] FIG. 1 is a flow chart of a method for exploring a skarn-hydrothermal vein iron polymetallic ore in a plateau desert area according to an embodiment of the present disclosure.
[22] FIG. 2 is a planar graph of a AT contour line in a 1:50,000 high-accuracy magnetic survey of a Yemaquan area.
[23] FIG. 3 is a contour map of a 1:50,000 residual gravity anomaly of a Yemaquan area.
[24] FIG. 4 is a comprehensive inference and explanation map of a GY3 in a WFEM of a Yemaquan area.
[25] The technical solutions of the embodiments of the present disclosure are clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are merely a part rather than all of the embodiments of the present disclosure. All other examples obtained by a person of ordinary skill in the art based on the examples of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.
[26] An objective of the present disclosure is to provide a method for exploring a skam-hydrothermal vein iron polymetallic ore in a plateau desert area, to solve the problem that ores cannot be accurately prospected under landscape restrictions and complex landforms in the plateau desert area.
[27] To make the above-mentioned objectives, features, and advantages of the present disclosure clearer and more comprehensible, the present disclosure will be further described in detail below with reference to the accompanying drawings and the specific implementations.
[28] As shown in FIG. 1, the method for exploring a skarn-hydrothermal vein iron polymetallic ore in a plateau desert area provided by the present disclosure includes the following steps:
[29] Step 101: Determine a type of a metallogenic system according to a spatio-temporal feature and a regional geological background in mineralization of a magmatic ore deposit and ore spot, and delineate a favorable mineralization zone of the magmatic ore deposit.
[30] Step 102: Carry out a 1:50,000 gravimetric survey on the favorable mineralization zone of the magmatic ore deposit, to delineate a gravity gradient belt.
[31] Step 103: Carry out a 1:50,000 high-accuracy magnetic survey on the gravity gradient belt according to a historical aeromagnetic anomaly inspection condition in the magmatic zone, to delineate a magnetic anomaly.
[32] Step 104: Carry out 1:2,000 electromagnetic profiling on the favorable mineralization zone of the magmatic ore deposit or the delineated magnetic anomaly to decompose the anomaly and narrow a target, and determine an anomaly distribution feature and a spatial position for positioning a magnetic body.
[33] Step 105: Verify, with a deep drilling technology, the anomaly distribution feature and the spatial position for positioning the magnetic body, and explore a change of a skarn iron polymetallic ore in grade, thickness, scale and occurrence.
[34] Step 106: Carry out a WFEM on a non-magnetic anomaly area between M1-M3 magnetic anomalies and the gravity gradient belt to separate a distribution range and a buried depth of each of a stratum and a rock mass.
[35] Step 107: Verify the distribution range and the buried depth of each of the stratum and the rock mass with the deep drilling technology, and explore a change of a hydrothermal vein polymetallic ore in grade, thickness, scale and occurrence.
[36] The iron polymetallic ore in Step 101 is dominated by an iron ore or an iron polymetallic ore, and accompanied by a nonferrous metal ore such as copper, lead and zinc ores.
[37] Or, the metallogenic system is a collisional and post-collisional orogenic mineralization system.
[38] Or, the metallogenic system is a skam-hydrothermal iron polymetallic ore system; the system delineates indosinian intrusive granodiorite and monzogranite associated with the iron polymetallic ore and the mineralization; and the metallogenic belt in the research area overall forms a skarn-hydrothermal iron polymetallic ore zone centered at the Yemaquan area as well as Sijiaoyang-Niukutou and Galinge iron polymetallic ore spots and iron ore spots, etc.
[39] The gravimetric survey in Step 102 is implemented by using a grid of 500*100 m and an advanced high-accuracy CG-5 gravimeter, acquiring field gravimetric observation data with a PPP, correcting each item, acquiring a bouguer gravity anomaly of each survey point at high quality, separating, with a reasonable data processing technology, anomaly information displaying different geologic structures, extracting and concluding qualitatively inferred local anomalies arising from different geofactors such as a structure and a rock mass, determining a contact zone between the rock mass and a stratum, and selecting the gravity gradient belt in combination with the gravimetric survey and the magnetic survey.
[40] Delineating the magnetic anomaly in Step 103 specifically includes: carry out positioning and the magnetic survey according to a theoretical coordinate by using a regular grid of 500*100 m, an advanced high-accuracy proton magnetometer and navigation and positioning functions of a handheld GPS during the 1:50,000 high-accuracy magnetic survey, automatically store surveyed data, correct a normal field and daily variation, formulate a magnetic survey series map, and delineate the anomaly.
[41] The 1:2,000 electromagnetic profiling in Step 104 is implemented by arranging a profile in perpendicular to a long-axis direction of the delineated magnetic anomaly, carrying out the high-accuracy magnetic survey at a point distance of 5 m with an RTK positioning technology, carrying out an inversion with geochemical inversion software to further know an anomaly feature in detail, and positioning the spatial position of the magnetic body with inversion and interpretation.
[42] In Step 106, the WFEM profiling is first carried out on known profiles of M1O and M13 magnetic anomalies having a high degree of geological control. The high-resistivity area corresponds to the rock mass, the low-resistivity area corresponds to the stratum, and the transitional area from the high resistivity to the low resistivity corresponds to the skarn zone or the contact zone between the rock mass and the stratum, deep spatial features of each geobody are reflected clearly, the rock interface is coincided with the actual interface of the prospecting line, and the iron polymetallic orebody is located in a conversion area from the high resistivity to the low resistivity. In order to research the non-magnetic anomaly area and the gravity anomaly gradient belt between M1-M3 magnetic anomalies, and find possible non-magnetic ores, the profile is arranged in perpendicular to a long-axis direction of the gravity, the line distance of 500 m and the point distance of 20 m are used, the distribution range and the buried depth of each of the stratum and the rock mass are finely obtained, and the polymetallic orebodies in a deep area are delineated.
[43] Determining a change of the deep area of the mineralized body in grade, thickness, scale and occurrence with the drilling technology to find the orebody or the deposit specifically includes: arrange a drill hole with the delineated magnetic anomaly, where the drill hole is specifically located in a mineralization enrichment zone of the magnetic anomaly with reference to occurrences and contact relations of the stratum and the rock mass, and the weak magnetic anomaly area and the gravity anomaly gradient belt are arranged according to former ore-bearing conditions and WFEM achievements; straight-hole drilling is provided, with an aperture of an opening hole being 110-150 mm and an aperture of a finished hole being 75 mm; the coring rock stratum has a core recovery rate of not less than 70% on each layer; the rock stratum within 5 m of the mineralized zone, important marker layer and ore layer has an average core recovery rate of not less than 80%; each exploitable thin ore layer (having a thickness of less than 4-5 m) has an average core recovery rate of not less than 80%, and the thicker ore layer has an average core recovery rate of not less than % sequentially every 5 m; the drilling sampling method uses a core splitting method, with a half of the rock core being delivered to a test unit as a basic analytical sample for processing and testing, and the other half of the rock core being preserved as an auxiliary sample or a reserved rock core for researching; the basic sample has a length of 1 m, a maximum length of not more than 1.5 m, and an actual weight error of not more than 10% of the theoretical weight; and the sample does not cross any layer, an edge sample is controlled on a roof and a floor, and through verification with the deep drilling and tracing control, the change of the orebody (mineralized body) in grade, thickness, scale and occurrence is determined to find the orebody or the deposit in the deep area.
[44] Specific embodiment:
[45] With the iron polymetallic ores in the Yemaquan area as an example, the embodiment describes the prospecting effects of combinations of prospecting technologies and methods.
[46] 1. Understanding on ore-forming material sources and ore-controlling factors of the skarn-hydrothermal iron polymetallic ores from the metallogenic system:
[47] Located in the Qimantage metallogenic belt, the Yemaquan iron polymetallic deposit is similar to the orefield in terms of the regional geological background, features of tectonic geology, exposed strata, intrusive rock masses and core-controlling factors; and this is also the case for the metallogenic system.
[48] (1) Material resources: The magmatic ore-bearing hydrothermal solutions evolved from magma of the Yemaquan deposit, and the ore-bearing substances and hydrothermal solutions occurred in the strata by metasomatism are migrated and enriched into ores. The metallogenic materials are derived from the magma and the surrounding rocks, and the ores have the features of the crust-mantle mixing source. Orebodies are generated in skarn in an external contact zone between the rock masses and the surrounding rocks and the skarn or skarnized carbonate rocks in the interlayer structural zone. From the intrusive rocks--skarnized intrusive rocks--skarn, contents of SiO 2 , A1 2 0 3 , K 2 0 and Na20 generally decrease, while the content of Fe203 increases. From the skarn--skarnized intrusive rocks->carbonate rocks, the content of CaO increases obviously, while the content of Fe203 decreases. It is indicated that when the skarn is formed by contact metasomatism, the CaO is derived from marbles, the SiO 2 , A1 2 0 3 , K 2 0 and Na2O are derived from the rock masses, and the Fe203 is derived from the hydrothermal solutions. Sulfur isotope results show that the sulfur is derived mainly from the magma and slightly from the surrounding rocks. From fluidic features of the Galinge deposit in the neighboring area, the quartz fluid inclusion has the features of the medium-high temperature fluid, and features of the magmatic hydrothermal fluids. Adjacent to the Yemaquan deposit and having the similar geological background of mineralization, the Sijiaoyanggou deposit in lead isotope composition features lead in the orogenic belt that is relevant to magmatism and mixed with mantle-derived lead and crust-derived lead, which explains that the ores in the Yemaquan deposit have the features of the crust-mantle mixing source.
[49] (2) Features of ore-bearing geobodies: From the intrusive rocks to the surrounding rocks, there are unaltered intrusive rocks, internal skarn (altered intrusive rocks), skarnized carbonate rocks, skarn, skarnized carbonate rocks (brecciated metasedimentary rocks) and carbonate rocks in sequence. The orebodies are derived mainly from the skarn in the outer contact zone between the intrusive rocks and the carbonate rocks, and partly from the skarnized carbonate rocks on the top. The former mainly possesses the iron, copper and zinc ores, and the latter mostly possesses the lead and zinc ores. The internal skarn is barely developed, with sparse distribution and weak mineralization. The ore-bearing rock strata are mainly the skarn and the skarnized carbonate rocks on the top.
[50] (3) According to the research, the deposit undergoes the skarn period, quartz-sulfide period and supergene oxidation period. It has the similar metallogenic characteristics and metallogenic process with the typical skarn deposit. The magnetite is mainly formed in the skarnized carbonate rocks during high-temperature stages of the late skarn period and the quartz-sulfide period. The polymetallic ores are formed in the medium and low temperature stages of the quartz-sulfide period, and formed into a thick vein with gangue to enter the magnetite.
[51] (4) Ore-controlling factors: The deposit is comprehensively controlled by the types of the intrusive rocks, the contact morphologies and contact zones between the intrusive rocks and the surrounding rocks, the lithology of the surrounding rocks, the structures, etc.
[52] I. Intrusive rocks:
[53] From the tectonic environment and deep mechanism in formation, intrusive rocks having different geotectonic backgrounds, magmatic sources and differentiation degrees play an important role in scales, types and varieties of the mineralization. Minerogenetic conditions of quartz monzobiorite and granodiorite for Fe, Pb and Zn ores are closely tied with the low magmatic differentiation, the large depth of origin, the oxygen-rich environment, and the strong crust-mantle substance exchange in the magmatic source. The monzogranite is dominated by Cu with a small scale of Fe ores, which is associated with the high magmatic differentiation, the crust substances mainly contributed by the magmatic source, the small depth of origin and the low oxygen fugacity. With the high differentiation degree, the iron is highly dispersed in the crystallized solid phase during magmatic crystallization and difficultly enriched in the magmatic hydrothermal solution, such that the mineralization ability of the iron ores is not strong. Conversely, the low differentiation degree is beneficial to formation of the iron ores.
[54] II. Intrusive morphologies of the rock masses
[55] The rock masses are intruded into the strata in the form of batholith, tongue and apophysis. The tongue mineralization is most favorable, with orebodies occurring as stratoids and large lenses and particularly having a large scale in depression zones. Scales and occurrences of the depression zones greatly affect the mineralization. Generally, in case of a large scale of the depression zones, the contact area between the rock masses and the surrounding rocks is expanded, which is beneficial to the mineralization. A gentle occurrence of the depression zones is also favorable to the mineralization. The tongue mineralization is represented by M4 and M5 magnetic anomaly areas. The batholith mineralization mostly forms laminal orebodies that are mainly located on the top and turning part of the rock masses, and is represented by M9 and MO magnetic anomaly areas. The apophysis mineralization is relatively poor, and mostly forms the vein, small lentoid and irregular orebodies. When the apophysis is branched and combined, small multilayer orebodies are formed.
[56] Lithology of strata and surrounding rocks:
[57] The surrounding rocks and strata are rocks in the Qimantage group and Di'aosu formation. Compared with the rocks in the Di'aosu formation, the Qimantage group has a high proportion to form the copper ores, which is mainly associated with the high background value of copper. As metasomatic surrounding rocks, the carbonate rocks are very favorable to contact metasomatism and hydrothermal metasomatism because of its active chemical property and high effective porosity. This is particularly the case for the carbonate rocks having impure components and silicification. The Di'aosu formation has the developed silicon-calcium interface, with a number of lead-zinc orebodies occurring in manganese skarn or skarnized carbonate rocks on the silicon-calcium interface. The silicon-calcium interface has the desirable mineralization because the silicon is not prone to the metasomatism to form the effective barrier layer and the magmatic hydrothermal solution fully contacts the calcium for metasomatism. Furthermore, it is also the tectonic weak zone to facilitate the migration of the mineralization hydrothermal solution. During the magmatic intrusion, the interface is fractured easily to form the interlayer slip and interlayer delamination, to facilitate the formation of an ore-accumulating structure, thereby being favorable to the contact metasomatism and hydrothermal metasomatism. Siliceous argillaceous rocks have a certain obstruction and isolation effect for skarnization and hydrothermal alteration because of its high content of inert components, inactive chemical property, low effective porosity, unfavorable solution permeation, strong rock plasticity and tough fracture.
[58] Contact zone:
[59] The contact morphology between the intrusive rocks and the surrounding rocks and the occurrence of the contact zone obviously dominate the scale and morphology of the orebodies. The occurrence of the contact zone is reverse to that of the surrounding rocks, and a larger included angle is favorable to the mineralization. In an area where the occurrence of the contact zone is the same as that of the surrounding rocks, the ore solution flows along the interface, which is unfavorable to the contact metasomatism. The contact zone with the slow occurrence, the contact zone where the intrusive orebody is located on the top of the stratum (overlap of the rock mass), and the estuary areas formed by contact of the rock masses (depression zones) are the most favorable areas to form the thick and large orebodies, such as the thick and large orebodies in the M5-1 magnetic anomaly area and M13 magnetic anomaly area in Yemaquan. This is because the contact area in these forms is large, and the estuary areas (depression zones) has the small stress to facilitate the accumulation of the ore solution. The contact zone formed between the intrusive rocks and the xenolith in the intrusive rocks has the large contact area, the thorough metasomatism and the large scale of orebodies and thus serves as the desirable ore-accumulating area.
[60] Tectonics:
[61] Faults in the orefield are well-developed, and falls into faults before mineralization, faults during mineralization and faults after mineralization according to the formation. Parallel displacement faults and reverse faults before the mineralization result in that metallogenic surrounding rocks vary for different zones. Due to lithological differences during the mineralization, degrees of contact metasomatism are different and thus the orebody scales are different or the orebodies are disconnected. With multi-stage activities and inheritance, the northwest-west trending fault group during the mineralization controls the trend, fold morphology, ore distribution and secondary tectonic distribution in the strata of the orefield, and is the main ore-controlling structure for south and north ore zones in the orefield. The northeast and northwest trending conjugate fault group communicates with the northwest-west trending fault and the interlayer structure perpendicularly, to facilitate the migration and metasomatism of the ore solution. It is the main ore-leading structure in the orefield. The interlayer structure and joint provide a desirable precipitation place for the orebodies and are main ore-accumulating structures in the orefield.
[62] 2. High-accuracy magnetic survey
[63] Magnetic features of rock ores:
[64] According to magnetophysical results in the orefield, the magnetite ores, magnetized skarn, pyrrhotized skarn, copper-lead-zinc mineralized skarn, magnetized homstone, chlorited and magnetized limestone and delafossite ores show strong magnetism. The magnetized hornstone presents the strongest magnetism, the pyrrhotized skarn is strong in magnetism but large in variation range and unstable in magnetism, and the magnetite has the relatively stable magnetism. In areas where the magnetite is distributed, the intensity and range of the magnetic anomaly are closely associated with the magnetite. The anomaly with a high intensity and a regular morphology indicate that the magnetic anomaly is mainly arising from the magnetite ores and the magnetized rocks. The skarnized limestone, homstone, tuff and diabase show intermediate magnetism and small variation range for anomaly, and mostly form the magnetic anomaly with the weak intensity and large variation. The biotite quartz schist, chlorited quartzite and biolite microclitic gneiss show the secondary intermediate magnetism, and typically lead to the small magnetic anomaly. Marbles and other carbonate rocks show the weak magnetism or no magnetism and mostly result in the stable background magnetic anomaly. According to results of the borehole three-component magnetic survey, the magnetite and magnetized homstone have the magnetic field intensity of positive and negative tens of thousands of nats, while the non-magnetized ores and surrounding rocks typically have the magnetic field intensity of positive and negative hundreds of nats, with few reaching to thousands of nats. There is the significant difference in magnetism between the magnetite orebodies and the surrounding rocks.
[65] Features of high-accuracy magnetic anomalies:
[66] Magnetic anomaly features and explanations and inferences: As shown in FIG. 2, 14 geomagnetic anomalies are delineated in total in the Yemaquan orefield, and numbered as M1-M14. According to the distribution range of the anomalies, there are south and north anomaly belts (ore zones). Located in a south shallow mountainous area of the orefield, the south anomaly belt has the serious coverage of wind-blown sand on the earth's surface, is distributed along a contact zone for granodiorite, monzogranite and marbles in the carboniferous Di'aosu formation, is of a south-protruding horseshoe shape with a length of about 13 km and presents five magnetic anomalies (M1, M2, M6, M9 and M10). Located in the north coverage area, the north anomaly belt basically has no outcrop on the earth's surface, and is controlled by the northwest-west trending fault with a length of multiple kilometers. The north anomaly belt is covered by quaternary gravel with a thickness of about 40-70 m, and presents nine magnetic anomalies (M3, M4, M5, M7, M8, M11, M12, M13 and M14). The distribution and extension of the anomalies indicate the trend of a boundary line of the intrusive rock mass and the distribution range of the magnetized skarn. The geomagnetic anomaly curves are smooth and gentle with positive and negative anomalies. Some anomalies show the large intensity and sharp gradient, with the peak up to 8,000 nT; some anomalies show the intermediate intensity and banded morphology, with the peak being 1,000-3,000 nT; and some anomalies are gentle, with the peak being 370 nT. The strong magnetic anomalies are arising from the magnetite having a small buried depth and a large thickness, the gentle anomalies are arising from the pyrrhotite or the magnetite having a large buried depth, and the banded anomalies with the intermediate intensity are arising from the magnetized rocks (magnetized carbonaceous-calcareous slate, and magnetized basalt).
[67] Main anomaly features relevant to the mineralization are respectively described as follows:
[68] MI: Located in the south of M2 and M3 anomalies in the Yemaquan anomaly area, the anomaly is decomposed into 10 subanomalies by a 1:2,000 high-accuracy magnetic survey, with the morphology basically same as that of the former 1:5,000 geomagnetic anomaly. Mi-1, M1-5 and M1-7 anomalies are basically the same in nature, with the large scale and the smooth and gentle anomaly curve. They are weak magnetic anomalies, and present features of deep anomalies and a large scale of magnetic bodies. M1-2, M1-3, M1-4, M1-6 and M1-8 anomalies are basically the same in nature, with a length of 180-460 m, a width of 120-300 m and an intermediate scale, and feature the large intensity and the sharp gradient. Except that the Mi-1, MI-9 and MI-10 magnetic anomalies are not verified, shallowly buried iron polymetallic orebodies are seen in the M1-2, M1-3, MI-4, MI-5, MI-6, MI-7 and MI-8 anomalies. There are iron ores--iron polymetallic ores--polymetallic ores from the south to the north, and iron ores--iron-copper ores->copper ores--lead-zinc ores from the contact zone to the earth's surface. The orebodies present the stable extension, large scale and high grade, further indicating that the anomaly is potential to prospect the iron ores--iron polymetallic ores--polymetallic ores from the south to the north. Examples are described as follows:
[69] Analysis on the features of the typical MI-7 anomaly in the MI anomaly area: Located at a spring of the Yemaquan area, and having the north connected to the Mi-5 and MI-6 anomalies, the anomaly is north-northwest trending and is the weak magnetic anomaly with a large range and the smooth and gentle curve. It presents the features of the deep anomaly, and the AT maximal value changes between 250 nT and 800 nT. From the west to the east, the curve on two sides of the maximal value is gentle in the west and sharp in the east; and the intensity tends to be small, large and small from the south to the north. Through verification, three iron polymetallic orebodies are delineated.
[70] M3: Located in the northwest of the anomaly area and connected to the southeast M4, M5 and M7 anomalies, the anomaly is in a zonal distribution, with the west being the southwest trending anomaly, the east spit into the south and the east, the south connected to the MI and the east connected to the M8. From the morphologies of the anomalies, the M4 and the M5 have the high intensity, while the M3 has the weak intensity. The anomaly presents the elliptical distribution, sharp gradient, high intensity (8,000 Y), smooth and regular curve, high polarizability and low resistivity. In view of influences from the M1-6 and M1-7 in the east and west, the positive anomaly in the north is more than that in the south, and the magnetic bodies are south-southeast trending, with an inclination angle of 5°. In combination with engineering verification on the deep area, 39 iron polymetallic orebodies are delineated, with a length of 165-540 m and a thickness of 4.4-8.03 m. Therefore, it is inferred that the anomaly is arising from the outer contact zone between the deep rock masses and the strata.
[71] M9: Located in the central south of the anomaly area and connected to the M10, the anomaly is divided into five subanomalies by the 1:2,000 high-accuracy magnetic survey. The M9-1 and M9-3 anomalies present the large scale, which is caused by the magnetite through the drilling verification. There are two main orebodies. The M9-1 anomaly presents the southwest-west trending elliptical distribution mainly having positive values, sharp gradient and high intensity. The M9-3 anomaly presents the southwest-west trending zonal distribution mainly having positive values, accompanied weak anomaly with a negative value in the north, sharp gradient, and high strength with the maximal value up to 3,000 nT. The M9-2, M9-4 and M9-5 anomalies are northwest-west trending, consist of multiple elliptical anomalies, and are generally dominated by positive values, and slightly accompanied by strong negative values.
[72] M10: Located in the central south of the anomaly area and connected to the M19 in the west, the M1O magnetic anomaly is divided into 10 subanomalies, among which the M1O-6 subanomaly has the largest scale, followed by the M1O-5, M1O-7 and M1O-8, and the rest subanomalies present the small scale, low peak and lack of regularity. The M1O-6 consists of three banded anomalies and is northwest-west, northeast and northwest trending to form a triangle. There are the accompanied strong negative anomaly in the north, the sharp gradient and high value (3,500 nT) in the west, and the gentle gradient and low value in the middle. The M1O-5, M1O-7 and M1O-8 magnetic anomalies have the high peak and gentle gradient, and are generally dominated by the positive values. Though the drilling verification, 26 iron polymetallic orebodies are delineated in the deep area, including two main orebodies with a length of 373-1,245 m and a thickness of 4.24-7.31 m. The orebodies in the anomaly area are mainly derived from skarn in an outer contact zone between the granodiorite and the late carboniferous Di'aosu formation. They are thin tabular, northeast trending, and gentle in inclination angle that is often 5-20°. Therefore, it is inferred that the anomaly is arising from the outer contact zone between the magnetite, the rock masses and the strata.
[73] M13: Located in the quaternary coverage area in the northeast of the anomaly area, this anomaly is the positive magnetic anomaly most widely distributed in the area. Its plane is elliptical and its long axis is northeast-southwest trending and has a length of about 2,400 m and a width of 500-1,200 m. The anomaly trends to be pinch-out in the east, and reduces the amplitude and is branched in the west. It is consecutive to the east-west trending banded anomaly in the M1O magnetic anomaly. Nine magnetic anomalies with the high intensity, large distribution and smooth profile curve are delineated by the 1:5,000 high-accuracy magnetic survey, which indicates that the magnetic bodies have a certain buried depth. Through verification on the deep area, 90 iron polymetallic orebodies are delineated. The orebodies are located in skarn in the outer contact zone of the granodiorite, and their morphologies change with the contact zone. The buried depths in the south are small and less than 200 m, while those in the north are large and 300-600 m or even partly up to 900 m or more. The orebodies show the desirable consecutiveness, are mainly dominated by galena and blende, and have the length of about 1,500 m, an extended depth of 100-900 m, an average extended depth of 400 m, a general thickness of 1.44-6.04 m and an average thickness of about 3.14 m. The magnetite is enriched locally, with the thickness on the single layer up to 68.48 m. The main orebodies of the M13 magnetic anomaly are connected to the main orebodies of the M10 magnetic anomaly. With analysis on the magnetic substances, the high magnetic anomalies are mainly arising from the magnetite, skarn and homstone; and the skarn and homstone in the surveyed area are closely associated with the polymetallic mineralization. Therefore, the magnetic anomalies are of significance to indirectly prospect the iron ores and the iron polymetallic ores.
[74] 3. High-accuracy gravimetric survey
[75] According to the bouguer gravity anomaly in the Yemaquan orefield, the gravity is obviously low, the anomaly is basically trapped, and the contour lines at edges are dense. The anomaly with the low gravity corresponds to the quaternary strata and the intrusive middle-fine grained monzogranite and middle-fine grained moyite, the anomaly having the low gravity and locally having the high gravity on the background is an indication of a local distribution (residue) of the strata and the gravity gradient belt basically reflects the contact zone between the rock masses and the strata. This feature is clearer on the residual gravity anomaly map (FIG. 3). The area having the low gravity and locally having the high gravity on the background and the gravity gradient belt are favorable to mineralization. Through verification, the anomaly gradient belt is promising to prospect the ores.
[76] 4. WFEM
[77] In order to research weak magnetic anomaly areas and gravity anomaly gradient belts between the M1-M3 magnetic anomalies to find the polymetallic ores in deep areas, before the method is carried, a profile of the 52 prospecting line for the M1O and M13 magnetic anomalies is selected for test. The test indicates that each geobody has clear spatial features in the deep area, the rock interface is coincided with the actual interface of the prospecting line and the iron polymetallic orebodies are located in an area where the high and low resistivity is converted. The actual prospecting effect indicates that the WFEM can effectively separate boundaries between the rock masses and the strata. Six profiles are arranged in the M1-M3 (as shown in the figure).
[78] Hereinafter, the GY3 line is used as an example for descriptions: The GY3 line has a length of 4.52 km and a measurement point spaced at 40 m. The strata exposed on the earth's surface are the quaternary carboniferous Di'aosu formation and granodiorite. The inversion is carried out on the inference and interpretation map 4 (1-position and number of drill hole; 2-inferred geological boundary; 3-copper-lead-zinc orebody; and 4-lead-zinc orebody). The resistivity distribution on the inverted sectional view is high in the middle and low on two sides, which indicates the intrusive activities of the intrusive granodiorite in the middle. The shallow electrical layer in the profile has an inversion resistivity of 60-200 Q-m, which indicates that the earth's surface is dry and quaternary, with the general thickness of 0-50 m. The near-surface zone at middle points 72-76 of the profile has the resistivity anomaly with a small area, which corresponds to the vein geologically revealed at present. For an area having the resistivity of 10-300 Q-m in the inversion profile, it is deduced that the low resistivity anomaly is arising from the strata with the thickness increased from the north to the south in 400-2,500 m. The strata at the points 48-100 have the small buried depths within 200-500 m and the rock masses may be provided thereunder. This zone is favorable to find the iron polymetallic ores. The strata of the Di'aosu formation at the points 100-114 have the large buried depths, with floors buried in 500-2,300 m. The buried depths are increased to the north. The area having the resistivity of 300 Q-m or more in the inversion profile is inferred as the rock masses. The resistivity near the point 100 is protrusive upward, which is rightly coincided with the central point of the M5 magnetic anomaly. With exploitation on the iron polymetallic orebodies in the M5 anomaly, the zone has the desirable ore-bearing potential, which is coincided with the inversion achievement of the WFEM. According to the boundaries of the rock masses and the residual gravity anomaly gradient belts inferred by the WFEM, ZK52301 is provided at the point 59, and the rock mass herein may have a top depth of 350 m, thereby finding the polymetallic orebodies in the contact zone between the strata and the rock mass. By means of drilling, there are chalcopyrite-blende at 97 m, blende at 133 m, chalcopyrite at 240 m, chalcopyrite-blende-galena at 350 m, and the top of the rock mass at 376 m, and the ore-bearing potential is desirable. The actual rock interface is basically coincided with the inversely inferred rock interface (350 m), with the difference only being 26 m. The method finely separates the distribution ranges and buried depths of the strata and rock masses, further indicating that the weak magnetic anomaly areas and gravity anomaly positive-negative converted gradient belt in the M1-M3 magnetic anomalies provide good geophysical bases for the zone and expand the space to prospect the polymetallic ores in the deep area.
[79] 4. Inverse simulation of magnetic anomaly
[80] By comparing inversion with the drilling data and inversion without the drilling data on the profile of the 0 prospecting line of the M9 anomaly, it is found that orebodies inverted with the two methods are basically the same in morphology and occurrence, only tails of the orebodies are slightly different and the orebodies locally present a change in thickness, and the results of the two inversions are basically the same as the drilling verification. Overall, the inversion results are coincided with the actual condition. Upon this, inversion calculation is carried out on other magnetic profiles in the M9 anomaly area. The inversion results are helpful to the drilling, with the morphologies of the orebodies basically the same as those verified by the drilling, and also helpful to the ore depth and ore thickness. Therefore, the magnetic method in the area is the effective to prospect the ores.
[81] 5. Drilling
[82] With the 1:50,000 magnetic survey, 14 geomagnetic anomalies (M1-M14) are found in the Yemaquan area, and located in south and north anomaly belts according to the morphologies, intensities and located geological sites. The south anomaly belt is located nearly in the south of the orefield and distributed along the granodiorite, moyite and carboniferous marbles. According to results of the 1:50,000 gravimetric survey, the anomaly with the low gravity corresponds to the intrusive middle-fine grained monzogranite and middle-fine grained moyite, the anomaly having the low gravity and locally having the high gravity on the background is an indication of a local distribution (residue) of the strata and the gravity gradient belt basically reflects the contact zone between the rock masses and the strata. With further analysis and comparison, the magnetic survey and the gravimetric survey are explained with each other. Preferably, 1:5,000 or 1:2,000 high-accuracy magnetic survey is carried out on the magnetic anomalies such as the M1, M3, M9 and M13 while the anomalies of the high-accuracy magnetic survey are analyzed comprehensively and the anomaly features are explained at high accuracy, thereby further decomposing the anomalies and further narrowing the target. The 1:2,000 electromagnetic profiling, WFEM and inversion are used to further know the anomaly features in detail, and the inversion and interpretation are used to position the spatial positions of the magnetic bodies, such that the distribution ranges and buried depths of the strata and the rock masses are finely separated. The borehole survey provides bases for the ore prospecting. Through drilling verification, 228 iron polymetallic ore zones are delineated. It is cumulatively estimated that a large deposit is present, with the total amount of copper, lead, and zinc metals being up to 1,043,500 tons, and the amount of iron ores being about 44,554,600 tons.
[83] By testing exploration and prospecting technologies and methods in recent years, and taking the iron polymetallic deposit in the Yemaquan area as the key research object, the present disclosure delineates 14 anomalies, including seven ore-forming anomalies, three magnetic anomalies arising from the magnetite, and one anomaly arising from the volcanic rocks. A batch of iron polymetallic ore spots and mineralized spots are found in the peripheral and surrounding areas and thus a great breakthrough is made to find the iron polymetallic ores. According to geophysical prospecting achievements and drilling verification results of the orefield, the geomagnetic anomalies serve as the most direct and principal geophysical prospecting method to find the iron ores; gentle anomalies (more than 200 nT and less than 250 nT) are of significance to indirectly find the polymetallic ores; edge and deep contact zones with the low gravity (rock masses) and high gravity (strata) in the residual gravity gradient belt are most favorable to find the skarn polymetallic ores and particularly significant to find the polymetallic or iron polymetallic orebodies; the borehole magnetic survey reflects obvious anomalies on the orebodies, with widths and positions of the anomalies being coincided with the orebodies verified by the drilling, and can indicate the presence of near-well blind ores (magnetic bodies); and for the conversion site in weak magnetic anomaly belt and the gravity gradient belt and the non-magnetic anomaly area in the plateau desert zone, the WFEM can serve as a preferable ore prospecting method to find the polymetallic ores, thereby separating the distribution ranges and buried depths of the strata and the rock masses, and assisting in finding the deep polymetallic ores. Therefore, the method combined with the "metallogenic system+gravimetric survey+high-accuracy magnetic survey+electromagnetic profiling inversion+WFEM+drilling" has the desirable effect to prospect the skarn-magmatic hydrothermal iron polymetallic ores in the plateau desert area.
[84] Each embodiment of the present specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts between the embodiments may refer to each other.
[85] In this specification, several embodiments are used for illustration of the principles and implementations of the present disclosure. The description of the foregoing embodiments is used to help illustrate the method of the present disclosure and the core principles thereof. In addition, the person of ordinary skill in the art can make various modifications in terms of specific implementations and scope of application in accordance with the teachings of the present disclosure. In conclusion, the content of the present specification shall not be construed as a limitation to the present disclosure.
Claims (5)
1. A method for exploring a skarn-hydrothermal vein iron polymetallic ore in a plateau desert area, comprising: determining a type of a metallogenic system according to a spatio-temporal feature and a regional geological background in mineralization of a magmatic ore deposit and ore spot, and delineating a favorable mineralization zone of the magmatic ore deposit; carrying out a 1:50,000 gravimetric survey on the favorable mineralization zone of the magmatic ore deposit, to delineate a gravity gradient belt; carrying out a 1:50,000 high-accuracy magnetic survey on the gravity gradient belt according to a historical aeromagnetic anomaly inspection condition in the magmatic zone, to delineate a magnetic anomaly; carrying out 1:2,000 electromagnetic profiling on the favorable mineralization zone of the magmatic ore deposit or the delineated magnetic anomaly to decompose the anomaly and narrow a target, and determining an anomaly distribution feature and a spatial position for positioning a magnetic body; verifying, with a deep drilling technology, the anomaly distribution feature and the spatial position for positioning the magnetic body, and exploring a change of a skarn iron polymetallic ore in grade, thickness, scale and occurrence; carrying out a wide-field electromagnetic method (WFEM) on a non-magnetic anomaly area between M1-M3 magnetic anomalies and the gravity gradient belt to separate a distribution range and a buried depth of each of a stratum and a rock mass; and verifying the distribution range and the buried depth of each of the stratum and the rock mass with the deep drilling technology, and exploring a change of a hydrothermal vein polymetallic ore in grade, thickness, scale and occurrence.
2. The method for exploring a skarn-hydrothermal vein iron polymetallic ore in a plateau desert area according to claim 1, wherein the metallogenic system is a magmatic iron polymetallic ore system.
3. The method for exploring a skarn-hydrothermal vein iron polymetallic ore in a plateau desert area according to claim 1, wherein the delineating a magnetic anomaly specifically comprises: carrying out positioning and the magnetic survey according to a theoretical coordinate by using a regular grid of 500*100 m, a high-accuracy proton magnetometer and navigation and positioning functions of a handheld global positioning system (GPS) during the high-accuracy magnetic survey, and delineating the magnetic anomaly according to surveyed data.
4. The method for exploring a skam-hydrothermal vein iron polymetallic ore in a plateau desert area according to claim 1, wherein the gravimetric survey is implemented by using a grid of 500*100 m and a high-accuracy CG-5 gravimeter, acquiring field gravimetric observation data with a precise point positioning (PPP) technology, and delineating the gravity gradient belt according to the gravimetric observation data.
5. The method for exploring a skarn-hydrothermal vein iron polymetallic ore in a plateau desert area according to claim 1, wherein the 1:2,000 electromagnetic profiling is implemented by arranging a profile in perpendicular to a long-axis direction of the delineated magnetic anomaly, carrying out the high-accuracy magnetic survey at a point distance of 5 m with a real-time kinematic (RTK) positioning technology, carrying out an inversion with geochemical inversion software and positioning the spatial position of the magnetic body.
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FIG. 1 1/4－
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FIG. 2 2/4－
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FIG. 3 3/4－
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FIG. 4 4/4－
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114415244A (en) * | 2022-01-13 | 2022-04-29 | 青海省第三地质勘查院 | Sea phase sedimentary manganese ore exploration method |
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2021
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114415244A (en) * | 2022-01-13 | 2022-04-29 | 青海省第三地质勘查院 | Sea phase sedimentary manganese ore exploration method |
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