Graphite Exploration Methods Graphite Exploration - CSA Global

Graphite exploration methodsGraphite exploration– the importanceof planningGraphite has become the focus for dozens of exploration companiessince the mineral’s investment boom of 2011-2012. Andrew Scogings,Industrial Minerals Consultant*, looks at the different exploration andtesting methods and reporting conventions used by the graphite industry.Graphite exploration follows asimilar path to other minerals,often from discovery of an outcrop,which is then explored by methodssuch as field mapping, trenching,geophysics, drilling, assaying of the graphite contentand mineralogical and metallurgical testing.Data generated in this way, if successful, canlead to the estimation of a mineral resource.At the bare minimum, this defines the geometry,tonnage and the graphite content of the deposit.Most of the recent exploration activity hasfocused on flake graphite deposits whichgenerally occur in tabular or lens-like bodies;these may vary greatly in thickness and rangefrom sub-horizontal to steep-dipping. Thepurpose of this article is to provide anoverview of a road-map to success, based onsome fundamental steps through theexploration process for flake graphite deposits.Exploration geophysicsTable 1: Minerals likely to interfere or mask graphite assay by LOI methodMineralDecompositionTemperatureWeight loss( 010.1TalcDehydroxilation850-10004.8Source: Mitchell, 1993 (BGS)Geophysical techniques are an indirect way oftracing geological and/or mineralisationtrends across an exploration project. Giventhat graphite and associated metal sulphideminerals – for example pyrite and pyrrhotite– are conductors, various electromagnetic(EM) methods can be highly effectiveexploration tools for graphite mineralisation.EM surveys can be carried out on the ground,downhole or from the air.Ground surveys can be performed by severalmethods, including fixed loop (FLEM) ormoving loop. Downhole EM surveys(DHEM) can be used to locate conductivetargets that may have been missed by a drillhole. Airborne EM surveys, such as versatiletime-domain electromagnetics (VTEM), arecommonly used during the early stages ofexploration as large areas can be coveredquickly and relatively cost-effectively.An example of VTEM anomalies that havebeen successfully explored by drilling is givenin Figure 1.Exploration trenching and drillingIMX Resources LtdFigure 1: Map showing VTEM anomalies, collar positions and the Chilalo mineral resource underdevelopment by IMX Resources Ltd (outlined in black). Map grid 1,000 metres42INDUSTRIAL MINERALSOutcrops of weathered graphite schist may besampled by excavating trenches, or by cuttingchannels across un-weathered outcrops, usinga portable disk grinder (Figure 2). Thesemethods provide a reasonably inexpensive wayto trace mineralisation across a propertybefore drilling.There are two main methods of drilling forgraphite, namely reverse circulation (RC) anddiamond core drilling (DD), each of whichhas its own advantages and disadvantages.Auger drilling may occasionally be used toexplore highly-weathered clayeymineralisation.December 2015

Graphite exploration methodsRC is a type of percussion drilling that usesa hammer to pulverise the rock into powderand chips, which are brought to the surface bycompressed air (Figure 3). RC is a useful wayof infill drilling between DD section lines todemonstrate geological and grade continuity,as it is quicker and less costly than DD.DD is however the preferred method ofexploration drilling for graphite, as thegraphite flakes and host rock are relativelyundisturbed when retrieved as core (Figure 4).Many exploration companies employ bothRC and DD methods to optimise drillingdensity.Bulk densityDecember 2015Figure 3: RC chip samples at Kibaran Resources Ltd’s Epanko graphite project, TanzaniaIMX Resources LtdBulk density is a measure of mass per unitvolume of rock. In the mining industry, this isgenerally referred to as metric tonnes percubic metre, or pounds per cubic foot.Graphite resources are typically modelled asvolumes in three-dimensional space, afterwhich the estimated volume is converted tomass using density values. Density can beexpected to vary across a graphite deposit,from low density weathered mineralisationnear surface through a denser transitionalzone and finally into the densest fresh(un-weathered) rock.Determining bulk density from smallsamples is something often faced bygeologists, who might only have drill coresamples to use for density measurement.There are several methods available todetermine volume of a sample, includingFigure 2: Channel sampling of a graphitic outcrop in CanadaKibaran Resources LtdThe old computing adage of “garbage in,garbage out” is highly appropriate in themining industry, which relies on minisculesample sizes (such as drill cores) to makeimportant decisions regarding the set-up of amining project.Quality assurance (QA) is put in place toprevent problems, while quality control (QC)aims to detect them in the event that theyoccur. It is necessary to insert samples knownas standards, blanks and duplicates into thesample sequence that is submitted to alaboratory. A set of samples should also besubmitted to another (external) laboratory forcheck, or umpire assays.QC data may be visualised in a number ofways including tables, control charts (Figure5), histograms, scatterplots or quantilequantile (QQ) plots.Twinned holes are traditionally drilled forverification of historic data or confirmation ofdrill hole data during geological due diligencestudies. When drilling out a resource, aselection of RC holes must be twinned withDD holes, as the soft and low density graphitemay be lost as fine dust from RC samples andcause an assay bias.Ardiden LtdQuality assurance and quality controlFigure 4: DD core samples of high-grade flake graphite mineralisation in a core trayINDUSTRIAL MINERALS43

Graphite exploration methodswater displacement (the “Archimedes”method) or the caliper method, in which corediameter and length are measured and fromwhich the volume can be derived.Highly weathered drill core presents achallenge, as it may not be possible to removethe core intact from the core tray for volumemeasurement. In this case, an entire tray withcore can be weighed, from which the weightof an empty tray is subtracted to give theweight of core. The core volume is thendetermined using the calliper method.Table 2: Mineral resource classification based on the JORC Code 2012CriteriaInferred resourceIndicated resourceDoes the resourceestimate supportthe application ofmodifying factors?Must not beconverted to anore reserve.Supports detailedSupports mine planningmine planning and finaland economic evaluation.economic evaluation. CanCan be converted tobe converted to a provedprobable ore reserve.or probable ore reserve.Measured resourceQuality ofinformationLimited geologicaland samplingevidence.Adequately detailed andreliable geological andsampling evidence.Detailed and reliablegeological and samplingevidence.Geological andgrade continuitybetween pointsSufficient to implybut not verify.Sufficient to assume.Sufficient to confirm.Assaying for graphitic carbonCarbon may be present in rocks inseveral different forms, including organiccarbon, carbonates or graphitic carbon.Depending on the method used, carbon inrocks may be reported as total carbon (organiccarbon carbon in carbonate minerals carbon as graphite) or as total graphitic carbon(TGC) (total carbon – (organic carbonatecarbon)).The simplest way to analyse a sample forgraphite is by loss on ignition (LOI), in whichcase a sample is heated to 1,000oC and thegraphite content is determined as thepercentage weight loss. However, otherminerals – such as calcite that contain carbondioxide (CO2), or clay and mica that containstructural water – will contribute to weightloss, resulting in apparently higher graphitecontent than anticipated (Table 1).Therefore, when TGC is reported, organiccarbon and carbon in carbonate minerals suchas calcite should be removed before assayingTGC. Different laboratories use differentprocedures for measuring graphitic carbon,which is the reason for inserting standardsinto the sample stream and also for sending aset of samples to an external, or umpirelaboratory.Source: Jacqui Coombes (pers. comm.); IMR Natural Graphite ReportFigure 5: Graphite standard GGC06 submitted with drill samples**** Expected value 7.68% graphitic carbon; sample mean 7.81 % graphitic carbonSource: Scogings and Coombes, 2014Mineralogical examinationLamboo Resources Ltd; CSA Global Pty LtdFigure 6: Polished thin sections. DD core on the left, RC chips on the right44INDUSTRIAL MINERALSSamples may be analysed for graphitic carbonand other elements, in addition to examiningthin sections under a petrographicmicroscope. Petrographic examination ofpolished thin sections (Figure 6) using anoptical microscope is a relatively affordableand quick way of estimating the in situgraphite flake size distribution and likelyliberation characteristics.Polarised-light microscopy is usuallycomplemented by methods such as X-raydiffraction (XRD), QEMSCAN (quantitativeevaluation of minerals by scanning electronmicroscopy) and mineral liberation analyser(MLA, or automated SEM).Mineralogical examination helps withgeometallurgical domaining of graphitedeposits and selection of composites formetallurgical testing. Sulphide mineralssuch as pyrite are common impurities inDecember 2015