CA1122107A - Method of processing samples of sedimentary deposits characterized by unstable sulphide conditions as an aid to detection of economic mineral content therein - Google Patents

Abstract

METHOD OF PROCESSING SAMPLES OF SEDIMENTARY DEPOSITS
CHARACTERIZED BY UNSTABLE SULPHIDE CONDITIONS
AS AN AID TO DETECTION OF ECONOMIC MINERAL CONTENT THEREIN

A B S T R A C T

A method of processing a bulk sample of a sedimentary deposit collected from a survey site charcterized by unstable sulphide conditions as an aid to the detection of economic mineral content in the sample is described. The method involves the steps of washing and wet sieving the sample to produce two or more size fractions, drying at least one size fraction, and separating that size fraction into at least two specific gravity fractions and, in at least some cases, magnetically separating at least one specific gravity fraction to produce a paramagnetic fraction. An acid leach step is included following specific gravity separation and is applied either to at least a part of a specific gravity fraction or, in cases where a paramagnetic fraction is produced, to at least a part of the paramagnetic fraction.

Description

This invention xelates to the field of mineral exploration. More par-ticularly, this invention relates to methods of processing bulk samples o~ loosely consolidated or unconsolidated "sievable" sedimentary deposits collected from survey sites characterized by unstable sulphide conditions to obtain fractions of such samples which fractions are suitable for analysis by means of a variety of conventional analytical techniques to detect anomalous economic mineral concentrations in the fractions. The samples normally contain only a minute amount of the economic mineral or minerals.
Herein, the term "mineral" or "minerals"
includes weathering products of the mineral or minerals. Also, it is to be understood that the word "sievable'l in reference to a sample indicates that the sample comprises particles of a size generall~ less than -6 mesh. In most cases, it is contemplated that a sample will comprise particles of a size generally less than -10 mesh. Howe~er, some minerals, such as diamond indicators may fall within the -6 to -10 mesh range. It is also to be understood that the present invention contemplates, in some cases, that a sample in the form originally retrieved from a survey site may in fact be in a semi consolidated state. For example, sediments collected from a dry creek bed may have been in a semi-consolidated state while ln situ. In such

- 2 -cases, it is to be understood as implicit that, prior to the application of the present invention, the semi-consolidated particles are loosened (viz.
as by agitation or light crushing) to separate the particles to an unconsolidated state.
A common method of processing a bulk sample of a sedimentarv deposit is to simply screen tne sample to produce a size fraction consis-ting o~ particles not greater than a predetermined size. OEten, the size fraction selected will be of the order of -80 mes~. For the purpose of concentrating metallic or sulphide minerals which occur in bulk samples of stream sediments to sedimentary deposits derived from the erosion of geologic environments containing mineral deposits, somewhat more involved processes have been used.
For example, it has been shown that hand panned, -80 mesh, bromiformed, non-magnetic heavy mineral concentrates of some stream sediments in the despersion train of some mineral deposits will, upon analysis, produce an accentuated and longer geochemical dispersion compared with conventional -80 mesh concentration techniques. Such methods are thought to reduceoccurrences where dilution by waste or uneconomic particles lvizo gangue) results in economic mineral deposits not being detected by conventional geochemical techniques. However, despite the advantage of such methods, several geologic-climatic environments have been found

- 3 22~

where the methods were ineffective at concentrating ore minerals, and there was little or no advantage over conventional geochemical techniques.
The ineffectiveness of such heavy mineral concentration methods may be attributed to a number of different reasons. Firstly, sulphide minerals and some other metallic minerals are easily floated, and gossan particles are easily washed away during hand panning with water. Combining such problems with the inherent problems of human inconsistency can result in little or no effective concentration.
Another common problem occurs when the geologic environment being sampled contains para-magnetic minerals such as epidote or garnet. High proportions of such minerals can become concentrated with heavy particles thereby affecting background or only weakly anomalous geochemical responses in the sedimentary dispersion of mineral deposits.
The present invention provides an improved method of processing a sample of a sedimentary deposit in conjunction with an exploration survey, and is specifically adapted for application in cases where the geologic environment of the sedimentary deposit under consideration is characterized by unstable sulphide conditions. The survey is one wherein a sievable bulk sample of a sedimentary deposit con-taining a minute amount of an economic mineral is collected from a survey site characterized by unstable sulphide conditions, then processed and subsequently %~

analyzed to detect the presence of the mineral. The improved method is applied to at least a portion of the sample.
In a broad aspect of the present invention, a sievable sample of a sedimentary deposit character- -ized by unstable sulphide ~onditions is divided into a number of sample fractions. The sample is washed and wet sieved with water containing an additive to reduce particle cohesion to thereby obtain at least two size fractions of the sample. At least one of the size fractions so obtained is dried and then sep-arated with heavy liquid into at least two specific gravity fractions. At least a portion of one of the specific gravity fractions is then separated into a gangue fraction and an ore metal concentrate fraction by means of an acid leach. The ore metal concentrate fraction so produced may then be analyzed by conven-tional techniques to detect and identify the economic mineral sought to be cletected. Since there are a variety of well known techniques for analyzing and identifying any ore metal concentrate which is present, they will not be discussed in detail here.
In another aspect of the present invention, generally the same method as is set forth above is followed, however, the acid leach step is applled to at least a portion of a paramagnetic fraction of one of the specific gravity fractions. Of course, this implies a magnetic separation step prior to the acid leach. Following the acid leach, the resulting ore metal fraction may then be analyzed using conventional techniques.
Preferably, the acid leach step comprises the following series of steps. The fraction to which the acid leach is being applied is first sub-mitted to cold aqua regia digestion. Oxalic acid is then added to the digested portion and the resulting acid mixture is then boiled. The hot acid solution is filtered and the filtered solution is then evaporated to dryness to produce a solute which is subsequently heated to decompose free oxalic acid and to drive off water of hydration.
In unstable sulphide conditions where mineral deposits develop thick leached cappings or when utilizing oxidized glacial sediments, sulphide minerals may be entirely altered to limonite minerals that separate in paramagnetic fractions. If the geologic conditions are such that voluminous amounts o~ epidote, garnet, ferromagnesium minerals and oblique or other paramagnetic gangue minerals are concentrated in the paramagnetic fraction, geoch2mical metal contrasts can be weak or diluted below threshold.
In such conditions, an acid leach step as described above applied either to paramagnetic concentrates or to size, specific gravity concentrated sediments that have undergone no or one magnetic separation, can be utilized to substantially increase geochemical contrasts - thereby increasing the probability of detec~ion. In rare instances, it is contemplated ~2~

that limonite coatings on magnetite will occur, in which case the acid leach step may be applied to a combined magnetic and paramagnetic fraction.
The invention will now be described in more detail with reference to the FIGURE which is a generalized flow chart showing an example of typical steps involved and sample fractions isolated during the practise of the present invention.
Although there may not be any magnetic separation step in p~rticular cases, the FIGURE depicts a magnetic separation step for the purposes of illus-tration. The FIGURE does not depict an acid leach step because the placement of such a step in the flow will depend upon whether there is a magnetic separa-tion. The acid leach step may be applied to a specific gravi-ty fraction or to a paramagnetic frac-tion of a specific gravity fraction.
As a preliminary point, it should be noted that the method depicted in the FIGURE has been found to impro~e geochemical contrast and dispersion even without an acid leach step. ~owever, in cases where there are unstable sulphide conditions, the dilution of geochemical metal contrasts may still be excessive in which case the application of an acid leach step becomes desirable. Ordinarily, any step (such as an acid leach) that causes chemical breakdown o~ the mineral constituents of a sample would be considered undesirable. Information concerning any source from which minerals may have been transported may be lost.

2~

In prospec~ing or mineral exploration, it is generally desired to know the mineralogy or chemical composi-tion of the original sample particles while in situ, and not axtificially induced secondary mineralogy or chemical composition. Particular unaltered or pri-mary mineralogies enable characterization of favourable ore hosts from unfavourable ore hosts or unfavourable combinations of ore hosts. Because an acid leach may cause chemical breakdown, it will be desirable in most cases to expose to the acid leach only a portion of a sample raction which has not undergone an acid leach -thereby tending to preserve mineralogical or chemical informa-tion that might otherwise be destroyed.
The FIGURE will now be described generally without reference to an acid leach step. Then, the application of the acid leach step will be described.
General Apart from the acid leach step, the ~IGURE
shows the processing which a sample of loosely con-solidated or unconsolidated sediments containing a minute amount of economic minerals may typically undergo in conjunction with a mineral exploration survey. The sample may be, for example: a sample of stream sediments, a sample of a glacial drift deposit, or a sample of soil sediments.
The sample is first submitted to a washing and wet sieving stage using water. Preerably, the - water includes a chemical additive which acts to reduce any particle cohesion and to reduce the surface ~2;~

tension of the water. It has been found that liquid detergent soap or an alkaline emulsifying agent can be a suitable additive. When water is available ~or use, the sieving can be implemented entirely in the field, or entirely in the laboratory~ or in part in the field and in part in the laboratory. Under field conditions, portable sieves or sieve sets are normally used, while under laboratory conditions mechanical sieve shakers axe normally used.
The washing and wet sieving of the sample separates two or more size fractions of predetermined size~ In general, it will usually be desirable to separate more than two size fractions - the FIGURE
specifically depicts -the separation of five fractions, namely, a clay size fraction, a fine size fraction, a moderate size fraction, a coarse size fraction, and an oversize fraction. The sieve sizes are somewhat arbi-trarily predetermined, but can be ad~usted after meneralogical size studies to best suit the sampling conditions. For example, sieve sizes of 10, 20, 40, 60 and 80 mesh miyht be used initially, but subse~1lent analysis may reveal that the 40 to 60 an~ 60 to 80 mesh fractions contain the final size fraction yielding the highest geochemical contrasts. Microscopic size analysis of these two size fractions may indicate that most of the metal beariny material ranges between 45 and 75 mesh. Thus, in exploration sampling ~or new deposits under similar conditions, only the 45 tp 75 mesh fraction need be isolated and processed further.

Fractions which were undersi~e in relation to the 45 to 75 mesh fraction would be discarded or stored for possible future use.
Under all con~itions, an object of the washing and wet sievin~ stage is to classify the sedi-mentary sample in a manner which minimizes particle cohesion and which minimizes metal particle loss through process of flotation. It is preferable to wash and scrub the finest fraction in a manner which reduces particle cohesion and substantially removes relativel~ light, generally clay-sized particles.
This may be accomplished in the following manner: by rubbing a fine fraction in water containing the chemical additive (e.g. detergent soap or alkaline emulsifying agent) by hand against the ~ottom pan or collective container of the sieve set used; by patting by hand any floating particles beneath the surface of water for a period of about 30 seconds which gives sufficient time to allow most clay sized limonites and sulphides to sink to the level of the sample overlying the pan; and by slowly pouring from the sample all but the last small remaining portion of water containing relatively light clay and organic particles. This process may be repeated using addi-tional clean water until most of the clay and organic suspension are removed. Although much the same results can be accomplished by conventional desliming techniques, this is generally not preferred because very fine metal particles ma,v be lost in the slimes.
The amount of sediment collected in orien-tation sampling is initially arbitary, but generally sediments which contain 2 or more litres of -20 mesh sediments contain more than sufficient material. The amount of a particular size fraction used for pro-cessing is normally a unction of the maximum amount that can be effectively separated during the first stage of heavy liquid separation. For example, if a conven-tional heavy liquid separation tube is to be used and its capacity is 500 ml of 45 to 75 mesh sediments, then only 500 ml of heavy sediments directly overlying the 75 mesh sieve would be retained for drying. The remaining mostly lighter upper excess layer would be either discarded or stored.
It is possible to remove these light excess particles by hand, by using a scooping tool such as a spoon, or by hand or mechanical panning. Panning of sized sediments, ideally with a mechanical panner to eliminate humanistic variance and with a chemical additive ~e.g. detergent soap) ~o minimize sulphide flotation, while possible, is not preferred. This is because during sufficient sieve shaking with up~down and/or rotational actions, the desired heaviest portion of each size fraction will be already gravity or jig concentrated near the surface of each restrictive sieve or near the surface of the basal container of the sieve set used. Thus such panning should be unnecessary. Of course hand panning would be even less desirable than ~2~

mechanical panning. It might also be noted that panning of the fine siæe fraction produced on sieving is likely to effect losses of metal bearing clay sized limonite particles along with the light particles which overflow with panning.
Following the washing and wet sieving stage, the size fractions which have been produced and retained are submitted to an important drying stage. Drying is normally completed rapidly/ either naturally utilizing the sun or in an oven at a low temperature, preferably less than 45C. Slow drying over extended periods can cause the alteration of sulphide particles to limonites.
Heating the sediments at elevated temperatures ma~
cause the magnetic susceptability of metal limonite or gossan minerals to be increased. In general, such changes are undesirahle, but one or hoth such changes can be deliberately caused in circumstances where it is considered desirable to do so. For example, in a highly specific geologic environment where there is a voluminous concentration of weakly paramagnetic gangue particles compared to a group of base metal bearing particles, principally in the limonite form, it may he desirable to magnetize the limonites in order to magnetically separate the metal and gangue particles. Similarly, pyrite and some other gangue minerals may be magnetized on sufficient heating. In environments where such gangue minerals are abundant, it may be desirable to remove them and thereby accentuate any geochemical response attributed to ore minerals in fractions of weak magnetic susceptlbility.
If the dried samples are unconsolidated, they are then in condition for the stage of specific gravity separation. However, it may occur that light clays will not have been separated to the extent de-sired from the fine size fraction and, upon drying, -will adhere in semi-consolidated state to particles of the fine size fraction. In such cases, it i5 advantageous to first reduce clay particle cohesion, preferably by resieving the semi~consolidated clay and fine size particles in a dry state through the fine size fraction sieve. This procedure will tend to strip the adhering clay particles from the fine size particles, and consequently permit the light clay particles to float during heavy liquid specific gravity separation.
As is illustrated in the FIGURE, a specific gravity separation stage follows the drying stage.
Here, each size fraction which is submitted to speciEic gravity separation, is separated into two or more specific gravity fractions. As depicted in the FIGURE, the coarse size fraction, the moderate size fraction, and the fine size fraction, each undergo a two stage specific gravity separation. For each such fraction a light specific gravity fraction (viz. light S. G.
fraction), a moderate S.G. fraction, and a heavy S.G.
fraction are produced. Typically, for example, a light S.G. fraction may consist of particles having a specific gravity less than 2.8 to 3.0, a heavy S.G. fraction may consist of particles having a specific gravity greater than 3.2, and a moderate S.G. fraction ~ould consist of particles having a specific gravity intermediate the light S.G. fraction and the heavy S.C. fraction. The precise specific gravity at which a separation is made can be varied somewhat and will be selected having regard to the specific gravity of the minerals of economic importance which are sought t~ be detected. The number of specific gravity separations made may be sub~ect to time and cost considerations.
In many cases it is sufficient to complete a one stage specific gravity separation through agitation and settling in a heavy liquid having a specific gravity of 3.2 to 3.3. Here, the light S.G. fraction would consist of particles having a specific gravity less than 3.2 to 3.3 and the heavy S.G. fraction would consist of particles having a specific gravity greater than 3.2 to 3.3. There would be no moderate S.G.
fraction, intermediate the light and heavy S.G. frac-tion. The separation can be attained, for example, with pure methylene iodide or with methylene iodide diluted slightly with acetone. When all or nearly all the heavy sediments have settled out of the periodically agitated fluid, the sediments are drained onto filter paper utilizing a drain system device such as a clamped tube or a stop-cock. After the heavy particle sedi-ments are thoroughly washed with solvent, they are dried, generally in a fume hood or in an oven according to the previously discussed condition of drying. The steps of washing with solvent and subsequent drying are depicted generally in the ~IGURE. The light particles are then separated, preferably in the same manner as the heavy particles. Much of the methylene iodide is recoverable by filtration and/or by evaporation of any solvent present.
However, it is preferred to complete a two stage heavy liquid separation consisting firstly of a primary separation at a specific gravity of 2.8 to 3.0 with a liquid such as tetrabromethene or bromiform, or a solution of acetone and methylene iodide. This is implemented in a manner similar to the one staye approach, but using a liquid of lower specific gravity.
This step is followed by a separation of the resultant heav~ fraction according to the process described above utilizing a liquid having a specific gravity o 3.2 to 3.3.
~lthough the two stage approach can be a little more time consuming, less of the relatively expensive heavy liquid, me~hylene iodide, will ordi-narily be lost when bromiform or ~he even more econ-omical liquid, tetrabromethene, is used for the primary separation. In fact, the economics of using the less expensive liquids permits the use of more voluminous separation containers, thus enabling the treatment of increased amounts of sediments and thereby reducing the chances of failing to concentrate economic mineral particles from the sediments. When the heavy minerals undergo ~he second separation at a specific gravity greatex than 3.2, the sample size is smaller and, probably attributable to decreased interference by light particles, the relative concentration of metal particles is, as a rule increased over that concen-trated with the single stage approach~ Furthermore, an additional fraction, intermediate in specific gravity to the light S.G. fraction and the heavy S.G.
fraction, is collected.
In many environments, metal assays on such intermediate S.G. fractions are significantly lower in magnitude compared with assays on the heavy S. G.
fractions. However, in a specific weathering environment where, for example, a relatively large amount of sulphuric acid resulting from the breakdown of sulphides is produced, there is a tendency for light limonites or gossan particles to be formed in the intermediate specific gravity range.
In a specific environment where most of the sulphides or metallic minerals present were altered to such limonite minerals, it may be imperative to recover the limonite minerals. Recovery of the intermediate S.G. fraction by a two stage separation -tends to ensure that virtually all economic metal bearing minerals will be concentrated.
Provided that the specific gravity separations have been implemented with some care, the light S.G.
fraction should not contain significant economic heavy minerals. Therefore, the light fraction is usually not separated further. Instead, a portion thereof is submitted in the dry state for assay as a check on the quality of separations and the remainder is stored.
However, in the event that light economic minexals such as minerals of berylium, lithium and/or coal are sought, it is normally necessary to have additional specific gravity and/or electromagnetic separations (discussed below) on the commonly volumi-nous, light S.G. fraction. Such separations are com-pleted using the same concentration principles as usedfor higher specific gravity fractions except that the specific gravity separation mediums and the electro-magnetic field settings are changed in accordance with the specific gravity and magnetic properties of the light, economic minerals which are sought to be concentrated.
After the fractions produced by specific gravity separation have been washed with solvent.and dried, the clean, dry, unconsolidated concentrates of both the moderate S.G. fraction and the heavy S.G.

fraction may be submitted to ma~netic separations to produce a magnetic fraction, a paramagnetic fra¢tion, and a non-magnetic fraction. In the FIGURE, the abbreviations "MF", "PMF" and "NMF" mean magnetic fraction, paramagnetic fraction, and non-mag~etic fraction, respectively.
The magnetic fraction is first removed with the use of a covered hand magnet, a conventional sep-arator for separating hand magnetic minexals, and/or an electromagnet set at a weak electromagnetia field setting. The object is to remove magnetic particles such as magnetite, chromite and pyrrhotite from the remainder of the fraction, the reason being that the presence of significant quantities of magnetic min-erals unrelated to ore mineralization decreases geo-chemical contrast and dispersion thereby reducing the probability of ore detection. In addition, the presence of significant quantities of magnetic minerals tends to later plug some separators which utilize electro-magnetic field principles. This then reduces the efficiency of separation of paramagnetic minerals from non-magnetic minerals.
The non-magnetlc particles are separated from the paramagnetic particles by submitting the sample in a known gravitational field to an electro-magnetic field. This can be accomplished with a number of known types of separators at optimum settings resulting in a removal of heavy particles of low magnetic susceptibility such as most native minerals, sulphides, base metal carbonates, and accessory min-erals from particles of moderate magnetic susceptibility such as garnet, epidote, wolframite, monazite, limonite and ferromagnesium minerals. Different makes of separators, and even individual separators of the same make, may require different settings to accomplish the same job.
If there was no acid leach step, and in cases where little was initially known about the geologic area under consideration, all of the resultant magnetic, paramagnetic, and non-magnetic, sized, heavy mineral fractions are weighed so that after geochemical assaying the combined assay of any two or more fractions can be computed. Typically, there may be 21 fractions per sample, but this number may vary in accordance with the number or size, specific gravity and magnetic separations which are employed.
These fractions, the light S.G. fractions, the light clay size fractions and the oversize particles may be hand or mechanically split into two or more portions. Portions of fractions that are 80 mesh or finer are conventionally geochemically analyzed for the metal types being sought. Portions of fractions that are 80 mesh or greater are normally crushed to at least -80 mesh before geochemical analysis or assay.
The Acid Leach __ As discussed above, it becomes important to apply an acid leach step prior to geochemical analysis in cases where unstable sulphide conditions are present. In such conditions, a strong acid leach step applied to at least a portion of a paramagne-tic concentrate or to at least a portion of a size, specific gravity concentrated sediment that has undergone no or one magnetic separation can be utilized to increase geochemical contrasts.

_ 19 _ In the past, dry sieved sediments have been treated with oxidizing acids such as 1.5 N oxalic acid to produce leachates. Such treatments have not achieved widespread popularity as an exploration or reconnaissance tool because, if there are carbonates in the sediments sampled, the acids are neutralized and fail to liberate base metal values. In addition, the acids tend to consume clay minerals, particularly of the amorphous groups. As the clay content of lQ sediments on a regional exploration program is variable, the gangue consumed by the acids is variable, and therefore, the analytical results are variable.
In applying a strong acid leach step to sink concentrates subsequent to the specific gravity con-centration, any limestone or dolomite-carbonate type particles will have been removed from the concentrates.
In addition, all or nearly all o~ the clay minerals - will have been separated from -the concentrates by the washing and wet sieving and speci~ic gravity separation steps. ~s the concentrates consist mostly of resistant silicate or accessory minerals, strong acids can be applied without overwhelming proportions of gangue being consumed by the acids. This increases the chance of liberating metal cations from goethitic limonites, heavy base metal carbonates, and other secondary minerals which are found to be resistant to weak acid attacks.
It has been found that resistant secondary minerals are substantially digested when the concentrates are submitted to a cold aqua regia digestion for a period of about two minutes, adding 2N oxalic acid and boiling the acid mixture ~or about five minutes.
About 3 ml of aqua regia and 10 ml of 2N oxalic acid were used per gram of concentrate tested.
The resultant acid solution was then filtered hot through a filter paper and evaporated to dryness in a crucible~ Heating was continued in a m~ffle furnace of about 500C until the free oxalic acid was decomposed and the water of hydration driven off. After the leachate was cooled, it could then be ground and geochemically analyzed. As the proportion of any metals digested to gangue digested was greatly increased, geochemical contrast and therefore probability of detection was correspondingly increased.
The geochemical and/or assay results of a complete orientation and/or reconnaissance program that may re~uire the use of an acid leach step can be conventionally statistically anal~zed to determine the frætion or combination of fractions which produce the highest geochemical contrast and longest geochemical dispersion to background or threshold. The unassayed portions of the high contra~t fraction or fract1ons, as well as the unassayed portions of immediately under-size and immediately oversize fractions of the same magnetic-specific gravity type, can be sieved and/or microscopically studied to determine the upper and lower size limits of the contained metal bearing particles, ~2~

Depending on the types of mineral deposits which are sought, the undigested portions of the fractions may be submitted to a variety of analytical techniques such as X-ray, Geiger counter, binocular microscope, electrostatic, electron excitation, isotopic and/or ultraviolet light treatment.
Modifications and variants of the foregoing will readily occur to those skilled in the art. The invention is not to be construed as limited to the particulars of the proposals specifically described above, but is to be afforded the full scope defined by the accompanying claims.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a mineral exploration survey wherein a sievable sample of a sedimentary deposit containing a minute amount of an economic mineral is collected from a survey site characterized by unstable sulphide conditions, then processed and subsequently analyzed to detect the presence of said mineral, an improved method of processing said sample after collection for analysis, said method comprising the steps of:

(a) washing and wet sieving the sample with water containing an additive to reduce particle cohesion and thereby obtaining at least two size fractions of said sample;

(b) drying at least one of said size fractions;

(c) separating with heavy liquid said last mentioned size fraction into at least two specific gravity fractions; and, (d) separating at least a portion of one of said specific gravity fractions into a gangue fraction and an ore metal concentrate fraction by means of an acid leach.

- Page 1 of Claims -

2. In a mineral exploration survey wherein a sievable bulk sample of a sedimentary deposit containing a minute amount of an economic mineral is collected from a survey site characterized by unstable sulphide conditions, then processed and subsequently analyzed to detect the presence of said mineral, an improved method of processing said sample after collection for analysis, said method comprising the steps of:

(a) washing and wet sieving the sample with water containing an additive to reduce particle cohesion and thereby obtaining at least two size fractions of said sample;

(b) drying at least one of said size fractions;

(c) separating with heavy liquid said last mentioned size fraction into at least two specific gravity fractions;

(d) magnetically separating at least one of said specific gravity fractions to provide a paramagnetic fraction thereof; and, (e) separating at least a portion of said paramagnetic fraction into a gangue fraction and an ore metal concentrate fraction by means of an acid leach.

- Page 2 of Claims -

3. In a mineral exploration survey wherein a sievable bulk sample of a sedimentary deposit containing a minute amount of an economic mineral is collected from a survey site characterized by unstable sulphide conditions, then processed and subsequently analyzed to detect the presence of said mineral, an improved method of processing said sample after collection for analysis, said method comprising the steps of:

(a) washing and wet sieving the sample with water containing an additive to reduce particle cohesion and thereby obtaining at least two size fractions of said sample;

(b) drying at least one of said size fractions;

(c) separating with heavy liquid said last mentioned size fraction into at least two specific gravity fractions;

(d) magnetically separating at least one of said specific gravity fractions to provide a combined magnetic and paramagnetic fraction;
and, (e) separating at least a portion of said combined fraction into a gangue fraction and an ore metal concentrate fraction by means of an acid leach.

- Page 3 of Claims -

4. A method as defined in Claim 1, wherein said acid leach separation comprises the steps of:

(a) submitting said portion of said specific gravity fraction to cold aqua regia digestion;

(b) adding oxalic acid to the digested portion and boiling the resulting hot acid solution;

(c) filtering the resulting hot acid solution;

(d) evaporating the filtered solution to dryness to produce a solute; and, (e) heating the solute to decompose free oxalic acid and to drive off water of hydration.

5. A method as defined in Claim 2, wherein said acid leach step comprises the steps of:

(a) submitting said portion of said paramagnetic fraction to cold aqua regia digestion;

(b) adding oxalic acid to the digested portion and boiling the resulting acid mixture;

(e) filtering the resulting hot acid solution;

- Page 4 of Claims -(d) evaporating the filtered solution to dryness to produce a solute; and (e) heating the solute to decompose free oxalic acid and to drive off water of hydration.

6. A method as defined in Claim 3, wherein said acid leach step comprises the steps of:

(a) submitting said portion of said combined fraction to cold aqua regia digestion;

(b) adding oxalic acid to the digested portion and boiling the resulting acid mixture;

(c) filtering the resulting hot acid solution;

(d) evaporating the filtered solution to dryness to produce a solute; and, (e) heating the solute to decompose free oxalic acid and to drive off water of hydration.

- Page 5 of Claims -