RU2034313C1 - Process of search and evaluation of magmatic bodies of lamproyte composition - Google Patents

Abstract

FIELD: geophysical prospecting. SUBSTANCE: samples of bedrock are taken, their chemical composition is analyzed and geochemical coefficients are calculated by its results. Depth of erosion cut as well as content and lump sizes of diamonds in magnetic bodies of lamproyte composition are determined by certain relationships. EFFECT: improved authenticity of process. 1 dwg

Description

 The invention relates to the field of applied geochemistry and can be used at various stages of geological exploration, including operational exploration, as well as during geochemical revision of objects (dikes, tubes, sills) for their diamond content according to the analysis of geochemical, point or furrow samples.

 There is a method for isolating lamproite magmatic bodies and assessing their diamond content based on the results of mineralogical and petrographic studies and taking into account the temperature conditions for the formation of magmatic bodies [1] In this way, one can only distinguish the types of lamproites and determine the presence of diamonds in them.

 The closest to the invention in terms of features is a method for searching and evaluating magmatic bodies of kimberlite and lamproite compositions [2], including sampling of bedrock rocks, determining their chemical composition, calculating geochemical coefficients and judging by their values about the presence of magmatic bodies of lamproite and kimberlite compositions and their diamond content.

 However, the known method provides an approximate estimate and does not allow to determine the level of erosion cut of magmatic bodies.

To increase the accuracy of the method and expand the scope of its application, new geochemical coefficients have been proposed that allow, in the presence of spectral and chemical analysis of samples (two or three samples from the object), to give an opinion on the object belonging to lamproites; determine the level of erosive opening of the object: crater, diatreme, channel or parts thereof (upper, central, lower); determine the diamond content of the object: low, high and medium diamond, the expected diamond content in carats. To use this method, it is necessary to have spectral (lead, zinc, barium, strontium, manganese, titanium, chromium, nickel, yttrium, niobium, vanadium) and chemical (K ₂ O; Na ₂ O; TiO ₂ ; MnO, CaO, CO ₂ ; MgO) analysis of samples.

 Using the proposed method, it is possible to isolate not only lamproite tubes, dikes, but also geochemical anomalies developed over the products of lamproite magmatism. The method is based on a generalization of the analysis results (chemical, spectral) of more than 160 pipes and dikes of objects in Western Australia, Spain, Africa, tested on a number of pipes in Belarus and the Karelian-Kola region.

;

K

K₃

Для объектов лампроитового магматизма (даек, трубок, силл) устанавливаются четкие пределы изменения величин отношений указанных коэффициентов, а именно: К₁:K₂:K₃:K₄:K₅ 5:3:1:4:6.Lamproite magma is characterized by a unique combination of groups of elements: petrogenic, rare, rare earth, sulfide, lithophilic, radioactive, alkaline, which determines its geochemical specialization. An analysis of the distribution of the limits of the contents of these groups of elements in lamproites as a whole made it possible to establish a single regional regularity within their concentrations both in separate parts of objects and in the lamproite column as a whole. This made it possible to develop and test geochemical coefficients that distinguish lamproites from other geological formations (ultrabasites, carbonatites, metamorphites, etc.). The coefficients of the formation affiliation of objects of research (tube, dike, sill) in lamproites (CF) include:

;

K

K ₃

For objects of lamproite magmatism (dikes, tubes, sills), clear limits are established for changing the ratios of the indicated coefficients, namely: K ₁ : K ₂ : K ₃ : K ₄ : K ₅ 5: 3: 1: 4: 6.

На основе анализа структуры вертикальной геохимической зональности, выражающейся в дифференцированном распределении содержаний элементов по лампроитовой колонне в целом, так и в отдельных ее частях (кратере, диатреме, канале), введены коэффициенты зональности (К₆, К₇). Специализация лампроитовых пород различных гипсометрических уровней (кратера, диатремы, канала) отражает геохимическую эволюцию магматического расплава от начальных до конечных этапов его становления, которая выражается в дифференцированном накоплении легколетучих элементов: лития, свинца, калия в верхних и апикальных частях колонны, а труднолетучих (титана, марганца) в нижних областях. Это обуславливает наличие своеобразной геохимической зональности, количественным выражением которой являются величины отношений следующих групп элементов:
K₆

и K₇

С помощью отношения коэффициентов зональности К₆/К₇ определяют уровень эрозионного среза объекта не только лампроитовой колонны, но и отдельных ее частей. Геохимическая зональность отражает минеральную зональность, выраженную в форме нахождения элементов в минералах и их количественных соотношений.

Based on the analysis of the structure of vertical geochemical zonation, expressed in a differentiated distribution of element contents over the lamproite column as a whole, and in its individual parts (crater, diatreme, channel), zonation coefficients (K ₆ , K ₇ ) are introduced. The specialization of lamproite rocks of various hypsometric levels (crater, diatreme, channel) reflects the geochemical evolution of the magmatic melt from the initial to the final stages of its formation, which is expressed in the differentiated accumulation of volatile elements: lithium, lead, potassium in the upper and apical parts of the column, and hardly volatile (titanium , manganese) in the lower regions. This leads to the existence of a kind of geochemical zonality, a quantitative expression of which is the magnitude of the relations of the following groups of elements:
K ₆

and K ₇

Using the ratio of zoning coefficients K ₆ / K ₇ determine the level of erosion cut of the object not only lamproite columns, but also its individual parts. Geochemical zonality reflects mineral zonation, expressed in the form of the presence of elements in minerals and their quantitative ratios.

The limits of change in the value of the geochemical zoning coefficient K ₆ given in the diagram of the vertical geochemical model of the lamproite column regularly vary from the upper crater zone to its lower root from p. 10 ³ to p. 10 ^-4 with a vertical swing of the lamproite column from 1 to 1.5 km (drawing). The crater zone is characterized by the ratio K ₆ / K ₇ > 10 ⁴ , the diatreme zone 10 ² <K ₆ / K ₇ <10 ³ ; the zone of the supply channel K ₆ / K ₇ <10 ² .

 The drawing shows the rocks found in the lamproite column: 1 shale, 2 tuffs, 3 sand tuffs, 4 massive igneous rocks.

After determining the lamproite type of magmatism and its level of erosion, it is equally important to establish or isolate among them potentially diamondiferous ones by preliminary determining the diamond contents in cr / t and the expected crystal sizes. This is the most difficult stage when sorting lamproite magmatism products. According to experimental data, diamonds crystallize under certain thermodynamic conditions due to the release of juvenile carbon at the boundary of chromium (peridotite) and titanium (eclogite) associations from the residual enriched fluidized and carbonated alkaline melt. Consequently, the amount of CO ₂ and CaO plays a significant role in the formation of diamondiferous lamproites. Analysis of the distribution of the limits of the contents of these elements: CaO x CO ₂ ; as well as Na, K, Mg, Cr, Ni, etc., and their oxides showed a direct relationship between diamond content with the content of Cr, Ni, Ca x xCO ₂ , Mg and the inverse with K ₂ O, Na ₂ O. The analysis was carried out for more than 160 tubes of Africa, Australia, Spain and showed good convergence of results.

K₉

K₁₀

Из результатов обработки материала по лампроитам и отдельным их видам следует:
1. При значении произведения К₈ ˙ К₉ x К₁₀ > 10⁵ трубки высокоалмазоносные. Содержание и размеры кристаллов больше 1 карат на тонну. Могут присутствовать при этом ювелирные разновидности кристаллов. Основные алмазоносные трубки Аргайл, Элендейл имеют значение К₈ больше 6 ˙ 10², среднеалмазоносные 1.10² и выше, слабоалмазоносные от 1 ˙ 10¹ и выше. Неалмазоносные имеют значение К₈ меньше 1 ˙ 10¹. Величина К₈чаще указывает на содержание алмазов в породе. Даже усредненные значения К₈ по 100 и более анализам подтверждают указанную закономер- ность.For geochemical constructions that determine the scale of the potential diamond potential of the object, the intensity coefficients (diamond content) of the object are calculated:
K ₈

K ₉

K ₁₀

From the results of processing the material for lamproites and their individual types follows:
1. With the value of the product K ₈ ˙ K ₉ x K ₁₀ > 10 ^{5 the} tubes are highly diamond-bearing. The content and size of crystals is more than 1 carat per ton. Jewelry crystals may be present. The main diamond-bearing pipes Argyll and Elendale have a K ₈ value of more than 6 ˙ 10 ² , medium diamond-bearing pipes 1.10 ² and above, and weakly diamond-bearing pipes from 1 ˙ 10 ¹ and above. Non-diamondiferous ones have a K ₈ value of less than 1 ˙ 10 ¹ . The value of K ₈ more often indicates the diamond content in the rock. Even the averaged values of K ₈ for 100 or more analyzes confirm this pattern.

The dependence of the diamond intensity coefficient on the scale of the dimension of diamonds in the tubes is established. So, the value of K ₉ for high diamond tubes is greater than 1 ˙ 10 ³ .

The same pattern is confirmed by the average values of the tubes for 100 or more analyzes. The geochemical coefficient K ₉ more often reflects the dimension of crystals. When K ₉ > item 10 ^{2, the} size of the crystals is expected to exceed 1 carat.

The most informative geochemical coefficient indicating the scale of mineralization is the value of K ₁₀ .

The coefficient K _{10 is the} most economical, express. All large diamondiferous tubes have K ₁₀ > 1 ˙ 10 ² ; medium diamond-bearing K ₁₀ 2 ˙ 10 ¹ and above; small and non-diamond-bearing tubes are characterized by K ₁₀ <1 ˙ 10 ¹ . Even large values of the geochemical coefficient of intensity clearly record a different degree of diamondiferous objects. So, Elendale 16 and Argyle are highly diamondiferous objects located in the region corresponding to the value of K ₁₀ 1 ˙ 10 ² and higher; for Nunkanbach and Wandigi K ₁₀ <1 ˙ 10 ¹ .

 Thus, the proposed method allows with high accuracy to determine the location of the magmatic body of the lamproite composition, to determine the level of its erosive cut, to reveal the presence of diamonds in it, to determine their number and size.

Claims (1)

METHOD FOR SEARCH AND EVALUATION OF LAMPROITE COMPOSITION MAGMATIC BODIES, including sampling of bedrock rocks, determination of their chemical composition, calculation of geochemical coefficients and judging by their values of the presence and value of diamond content of lamproite magmatic bodies, characterized in that geochemical coefficients K ₁ = ( MgO) ² (K ₂ O · Na ₂ O); K ₂ = Cr · Ni / Pb · Zn; K ₃ = Cr · Ni / Sr · Ba; K ₄ = Cr · Ni / Y ² ; K ⁵ = Cr · Ni / Nb ² , K ₆ = Pb ² / Ti · Mn; K ₇ = (K ₂ O) ² / TiO ₂ · MnO; K ₈ = CaO · CO ₂ / (Na ₂ O) ² , K ₉ = CaO · CO ₂ / Na ₂ O · K ₂ O; K _{1 0} = Cr · Ni / V ² , according to the value of the ratio K ₁ : K ₂ : K ₃ : K ₄ : K ₅ = 5: 3: 1: 4: 6 magmatic bodies of lamproite composition are distinguished, according to the value of the ratio K ₆ / K ₇ determine the depth of the erosion section, and according to the magnitude of the ratio K ₆ / K ₇ > 10 ⁴ , the crater zone is distinguished, 10 ² <K ₆ / K ₇ <10 ³ the diatreme zone, K ₆ / K ₇ <10 ² is the zone of the supply channel, and according to the value of the product K ₈ · K ₉ · K _{1 0} > 10 ^5, the diamond content in the magmatic body of the lamproite composition is more than 1 carat / t.

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