Process Development Metallurgical Studies

SPECIAL ISSUE ON PROCESS DEVELOPMENT TESTINGProcess development metallurgical studies for gold cyanidation process S. Acar Consulting metallurgical engineer (D.E.Sc.), Highlands Ranch, CO, USA Abstract In recent years the gold mining industry has been challenged by declining metal prices as well as having to treat ores that have low grades and are refractory in nature. Many factors must be considered when metallurgical studies are designed to develop process design criteria for these type of ores. These factors are mostly related to the mineralogical and chemical compositions of the ores, the geological setting of the deposit and how the ore/waste will be mined, such as whether openpit or underground, the mine schedule, and the mine fleet type and capacity. The purpose of this paper is to provide an experience-based practical approach to how to select and characterize test samples as well as devise process development metallurgical studies for both oxide and refractory gold ores, and to provide insight into some of the matters that might go wrong during the course of the studies. This paper is intended as both a guide for someone new to the field and also as a reminder for those familiar with the field. Minerals & Metallurgical Processing, 2016, Vol. 33, No. 4, pp. 161-171. An official publication of the Society for Mining, Metallurgy & Exploration Inc. http://dx.doi.org/10.19150/mmp.6837 Key words: Cyanide leaching, Gold processing, Refractory ores Introduction or siliceous refractory or any combination of those, that may The recent decline in ore grades and metal prices not be mined and processed economically due to reasons such have challenged mining companies to reduce capi- as the physical location of the deposit, depth of the ore lode, tal and operating costs associated with developing or social and environmental concerns. Therefore, an early col- new mineral resources. In some cases, metallurgical laboration between all disciplines must be established. studies have been sacrificed to prevent cost overruns Each orebody may have its own unique mineralogical, geo- resulting in inadequate mineralogical, chemical and logical and chemical characteristics (Guresin et al., 2012). These metallurgical characterization. Consequences have unique characteristics should be effectively sampled to reduce included longer construction schedules, higher initial risks associated with process design and engineering efforts for and working capital, higher operating costs and less the process development metallurgical studies. If the sample or than desirable plant performance (Whincup, 2010; samples are not representative of these unique characteristics, Torres, Chaves and Meech, 1999). then the studies performed will be pointless. The project met- Mineralogy, geology, mining type and sequence, allurgist in charge of conducting metallurgical studies should and the metallurgy of an orebody will determine the also possess general geology, mineralogy and mine engineering process development metallurgical study requirements knowledge. Recommended readings are a book on understand- and eventual process plant design. Therefore, once ing mineral deposits by Misra (2000) and articles on heap leach the geologist has an early indication of a prospective development by Scheffel (2014a and 2014b). orebody, geologists, metallurgists, mining engineers, and social and environmental responsibility scientists should convene and devise a plan on how to exploit the Process development metallurgical studies orebody economically (Lunt, Ritchie and Fleay, 1997). Developing a metallurgical program depends on the type of Geologists may find a prospective orebody solely ore under consideration. Gold ores may be divided into several based on grade. However, if the orebody cannot be categories (Marsden and House, 2006): mined and processed economically, then it is deemed 1. Oxide ores with or without coarse gold component. not to be a deposit. An example of this could be a 2. Refractory ores with or without coarse gold refractory gold deposit, either sulfidic, carbonaceous component: Paper number MMP-15-063. Original manuscript submitted August 2015. Revised manuscript accepted for publication May 2016. Discussion of this peer-reviewed and approved paper is invited and must be submitted to SME Publications Dept. prior to May 31, 2017. Copyright 2016, Society for Mining, Metallurgy & Exploration Inc. MINERALS & METALLURGICAL PROCESSING 161 Vol. 33 No. 4 • November 2016 2009).1 Zn<0.008<Au<0. Sulfide Cu>0. Therefore. 2004).01 opt Cu-2 Oxide Cu>0. The project metallurgist should always question. sample quality is extremely important for the development of a c.03<Au<0.1 <40 >40 Zn>0.1 <40 <40 c: Au>0. Dominy.5 >0. • Massive sulfide ores. • Telluride containing ores.1 <40 <40 Zn>0. obtaining the right samples • Pyrite.1 November 2016 • Vol.2 >0. Cu Acid.008 Zn>0.2 f: Au>0. Sulfide Cu>0.1 e: 0. ores with Sampling the deposit for metallurgical studies marcasite and/or pyrrhotite).1 oxide Cu-5 Oxide Cu>0.1 oxide Cu-11 Sulfide Cu>0. 2009. Carbonaceous refractory (preg-robbing) ores.1 a: CN/FA>40% Au-2 Oxide Au>0. metallurgical process for a particular deposit and troubleshoot- d.1 Zn-3 Sulfide Zn>0. Siliceous refractory ores.5 Zn-1 Sulfide Zn>0.5 <0. 33 No. arsenopyrite and arsenian pyrite — variability samples and master composites — for the process containing ores.03 Cu-4 Oxide Cu>0.1 Au-5 Sulfide Au>0. b. Sampling is conducted to assess geological and mineralogical • Enargite containing refractory ores.03 opt Cu. ing during operations (Chieregati and Pitard.03 Cu<0. Cyanide. 4 162 MINERALS & METALLURGICAL PROCESSING . Ore Au grade.1 >40 Zn<0. • High cyanide and oxygen consuming ores (copper containing ores.03 Cu-3 Oxide Cu>0.1 >40 Zn>0.1 b: CN/FA<40% Au-3 Oxide Au>0. High silver containing gold ores.1 >40 a: Au<0. Any combination of the above. “Is Table 1 — Ore types for a gold/copper/zinc ore deposit. abilities on metallurgical processes (Williams and Richardson.1 >40 Zn>0.03<Au<0.2 d: Au<0. Metallurgical studies conducted on the samples are only • Antimony containing ores.5 <0.1 >40 Zn>0.1 d: Au<0.1 f: Au>0.5 Copper ores Cu-1 Oxide Cu>0. variabilities within an orebody and the effects of these vari- • High elemental sulfur containing ores.1 b: oxide 0. Zinc Organic Lead Additional type opt grade soluble soluble grade carbon grade consider- (%) Cu:total Cu:total (%) content (%) ations Cu ratio Cu ratio (%) (%) (%) Gold ores Au-1 Oxide 0.1 Cu. Sulfide Cu>0.1 Zn<0.5 >0.03 opt Zn-2 Sulfide Zn>0.1 e: 12 0.1 13 Cu.01<Au<0.1 <40 <40 Primary 14 ore Zinc ores Zn-0 Oxide Zn>0. such as: Once the ore type is determined. a.1 Zn<0. attributable to the sample and what it represents. Sulfidic refractory ores. development metallurgical studies will easily be accomplished.2 >0.1 Zn-4 Sulfide Zn>0. 3. 2002). at cyanide-soluble copper contents — indicating different copper minimum. carefully considered when sampling the deposit for process Zinc ores are also divided into two types: oxide and sulfide. supergene which shows a long section of the deposit. plan and schedule. In most percent — with gold grades in excess of Au > 0. The oxide gold ore zone is further divided into several distinct ore types depending upon the process options. For example. The completed studies included: size and liberation characteristics. penalty • Whole ore roasting. copper ores are separated into two distinct ore samples. tory gold ores and ores containing copper and/or zinc 8. Chemical analysis. Depending upon availability. such as oxide versus refractory gold. geometallurgical domains.. Table 1. • Acid or bioleach followed by cyanide leach for copper ity sampling of a complicated gold deposit with copper and and/or zinc ores with gold credits. The metallurgical laboratory conducting the process devel- oxide versus hypogene copper. or cyanicides. one-half cut core is used for geochemical analysis and MINERALS & METALLURGICAL PROCESSING 163 Vol. Cu and Zn composites for process development 2. which may be called variability samples.01 > Au < 0. zinc metallurgical ore types may be identified as shown in • Bulk samples. including: gold ore zone and a zinc ore zone at depth. The length of the variability sample should be. • Column bioleach studies for copper and/or zinc sulfides. samples zinc contents for the sulfidic refractory gold ore type — indi- should be selected from geological sections that spatially cated by a Au(CN) to Au(FA) ratio that is less than 40 percent cover the orebody representing metallurgical. Woodhead and Smith. 33 No. In this deposit. ore type zones. including large-diameter The gold ore zone may be divided into an oxide and sulfidic metallurgical core. alteration. brecciation. 2013). Variability samples should not cross over different domains Cu2B ore type is defined as oxide heap-leachable copper ore and should include dilution. per assays. • Diamond core drilling samples. such as weathering. texture and grain size of a rock These ore types are schematically illustrated in Fig. preg-robbing • Flotation followed by concentrate treatment for refrac- gold assay. The mineable length will depend — having an acid-soluble copper to total copper ratio that is on the mining process. developmental testing (Guresin et al. Individual interval Similarly. divided into several subtypes depending upon the acid. and chemical and mineralogical • Grab samples.the sample representative of the orebody?” Au). and mineralogical and chemical analyses of the 3. the conducting of further laboratory Master composites may be prepared to fulfill requirements studies is recommended to recover gold post-acid leaching for extensive process development studies by combining several for oxide copper minerals. Changes in lithology — involving physical character. and geological changes: that is. cyanide soluble gold assay. • Column and agitated bottle roll cyanide leach studies for 6.5-m adit opening to 10-m bench height. to total gold. • Column acid leach studies for copper and zinc oxide ores. oxide. special attention should be paid to the faults. oxide gold ore zones are located closer to surface followed by the sulfidic refractory gold ore zone located at depth. For this ore type. The following items should be different gold grade ranges. 1. ratio. sulfides. Oxidation state — relative intensity of oxidation and individual variability samples. • Agitated bottle roll cyanide leach studies for oxide gold 7. master Au. Au2A ore type is defined as an oxide millable ore — Exploration departments may use the diameter sizes of NQ (48 indicated by a Au(CN) to Au(FA) ratio that is greater than 40 mm). such as fractures. 4 • November 2016 . Ore and gangue mineralogy — such as mineral particle process options for this deposit. and greater than 40 percent — with gold content of 0. opment study performed extensive studies to determine the 5. and valuable element deportment — and hardness. that may constrain throughput and recovery. hydrothermal alteration. spatial location. master composites alteration. the preference should al- such as heap leaching or milling based on the gold grade and ways be to use diamond drill core for variability samples and cyanide-soluble gold. characterizations as a guide. mineralogical — because they are known cyanide consumers.03 may vary from a 2. such as underground or openpit. options. lead and gold grades to determine process 1. zinc credits. Information on structure and texture. followed by cyanide leach for refractory gold ores. that is.and lurgical type. drill Sample types logs and drill interval assays indicates that the deposit also A diversity of sample types may be used during various stages contains a copper ore zone adjacent to the sulfidic refractory of metallurgical studies (Hanks and Barratt. sampling of this deposit would be. metallurgical studies. which demonstrates how complicated the variability • Reverse circulation drilling samples. Depth and spatial relations of different ore lodes and oxide gold ores to determine heap leachability. Mineralization type. transition and sulfide ores would be prepared to represent a mining horizon with similar (Hoal. For master composites during all stages of metallurgical studies. including valuable elements. example. Au(FA). istics such as color. pressure oxidation or biooxidation elements and process indicators such as sequential cop. Special attention should also be paid to the copper and For process development metallurgical studies. each containing three attention to spatial location. the following gold. mineralogy — zinc mineralogy and gold grades. A review of geological sections. Using available data such as lithology. When preparing alteration. HQ (64 mm) and PQ (85 mm) for core drilling.1 opt (3 g/t cases. 9. sulfidic copper ores may variability samples representing a given domain while paying be further divided into four subtypes. a mineable length and restricted to a given domain. The oxide copper ores are further taken across a zone to obtain a response to changes in metal. domains. should be zones: oxide and sulfide. A case study is presented here to demonstrate the variabil. As a result. Au(CN). opt. Mining method. Process options considered. copper and • Channel samples. Similarly. 4. unit — and alteration. grade variations. elements ores to determine milling. 2012): The sulfidic zinc ores are further split into zones with varying organic carbon. 33 No. than 300 ppm may also be measured for silver by fire assay.. November 2016 • Vol. Table 2 summarizes the sample lowing assays: weights available for cores of NQ. master composites. Most of the time. and (AuCN) procedure is an indicator of nonrefractory gold that Figure 1 — A geological long section showing gold. Gravity-recoverable gold content studies Cyanide-soluble gold assay. Hoffman. ALS Ltd. All variability samples and Silver assay. The chemical analysis may include the fol- some of the proposed studies. the following characterization metallurgical studies. If the gold content is Developing a metallurgical program exceeding 5 ppm. HQ and PQ sizes. 2014). benchmarked process flowsheet. all variability samples should required (McGuire. one-quarter cut core is stored as a catalog diagnostic leach studies may be conducted for ores are refrac- and the remaining one-quarter cut core is made available for tory in nature. fire assay with a gravimetric finish will be Once the samples are obtained. The cyanide-soluble gold may be conducted for ores containing free native gold. If the estimated gold assay is Au < 5 ppm. and the amount of drill core available is usually a sore point Chemical analysis.)-diameter metallurgical core to be drilled that will have impacts on cost and environmental liabilities to provide enough bulk sample and the top size required for (Dietrich. ogical characterizations. Gold by fire assay. 2012. copper and zinc variability samples as functions of depth. Samples with substantial silver content of more master composites must be subjected to chemical and mineral. fire as- say with AA finish should be requested. Gold by fire assay is the preferred method of analysis. including those or 150 mm (6 in. Comminution (crushing and grinding) although inductively coupled plasma is the preferred method characterization studies should also be conducted on select for Ag < 300 ppm. For all ore types. 4 164 MINERALS & METALLURGICAL PROCESSING . Chemical analysis must be conducted between the geologist and the metallurgist. on variability samples and master composites to determine the project metallurgist will require several additional PQ and/ minerals of value and deleterious elements. 1999).petrography studies. Variability samples should be prepared studies are recommended: for the metallurgical study using the quarter-cut drill core. Clark be prepared according to crush or grind sizes for the perceived and Yeager. 1989. 3 percent sodium cyanide (NaCN) cadmium (Cd). In sulfidic ores. and is used to estimate the acid neutralization potential of the ore. usually 0.4 1. The AuPR number. each one more aggressive and measured in combination with inductively coupled plasma.7 0. titanium (Ti).65 13. and metallurgical groups to quantify the primary ore minerals (St. and LECO instruments are used to determine as well as gangue and clay minerals. 2015). as needed for each project in collaboration with the geology LECO series of assays. vanadium (V). 33 No. 4 • November 2016 . cobalt (Co). as follows: Mineralogical characterization. which is calculated using equivalent to the Au concentration. uranium (U). scanning electron microscopy/mineral – AuPR (in g/t) liberation analysis (SEM/MLA). molybdenum (Mo). measurement is required for samples for both semiautogenous (SAG) mill comminution (SMC Testing. Morrell.3 1. is necessary for volatile elements.6 3. nickel content as determined through fire assay. A comminution charac- samples using a LECO infrared combustion analyzer. metallurgical process selection and environmental acid generation bond rod mill and ball mill indexes. Joseph. selenium (Se). How- except that it also contains a gold spike. Semiquantitative X-ray PRN = 3.. than the previous one. beryl­lium (Be). 2008). The sample weight and top carbon (AIC). It is identical to the AuCN protocol volved digestion followed by cold vapor measurement. 2016). large particulate native Au. The preg-robbing gold (AuPR) to also measure Sb. preg-robbing organic zirconium (Zr). Table 2 — Approximate sample weights for diamond drill cores with NQ. typically applies to any deposit method for Hg analysis is by using an Hg combustion analyzer. antimony (Sb). copper (Cu).85 6. bond abrasion index and potential estimation. containing organic carbon. also called acid-insoluble high pressure grinding rolls tests.5 2. zinc (Zn) and of sulfides. It is convenient Preg-robbing gold assay.270 Core diameter mm 45 61 83 Core size NQ HQ PQ Full Half Quarter Full Half Quarter Full Half Quarter kg 3. Elements including much of the periodic characterize gold association in the mineral matrix. manganese (Mn). bismuth (Bi). Core size NQ HQ PQ Core length meter 1 1 1 Density g/cm3 2. thallium difficulty due to several factors that may include the presence (Tl). chromium (Cr). The degree of preg-robbing may following the ASTM 6722-11 standard test method (ASTM be determined by the preg-robbing number. Se and tellurium in this same digestion. MI).5 3.75 7. and inductively interstage cyanide leaching to determine the amount of gold MINERALS & METALLURGICAL PROCESSING 165 Vol. by ratio. magnesium This AuCN value is then compared.4 Weight lb 7. while a PRN capacity (NIR/CEC) mineralogical requirements are determined greater than 3 indicates an ore that is extremely preg-robbing. lead (Pb). yttrium (Y). soluble gold to total gold will give an indication of leaching Tin (Sn). Traditional mercury (Hg) analysis in- gold capacity of the ore. obtained by determining the gold solubility of a pulverized arsenic (As). S-Sulfide. is used to predict the preg-robbing potential of an particle sizes required for the comminution characterization ore. The ratio of cyanide. sulfur. iron solution after 60 minutes of contact time in a shaker flask. aluminum (Al).875 14. (Fe). X-ray fluorescence (XRF). to the total gold (Mg). HQ and PQ sizes. PRN.1 opt Au ever. LECO is a trademark of LECO Corp.6 6.25 3. Organic carbon. gallium (Ga). 2002.5 Core recovery % 100 100 100 Void factor % 0 0 0 inch 1. (Ni). Diagnostic leaching is combined with optical emission spectrometry (ICP-OES). Hg is suppressed by an amount (3. rhenium (Re). 5-g sample in 10 mL of 0.8 3. Total carbon and sulfur contents should be measured for all Comminution characterization. Therefore the preferred the AuCN and AuPR assays. The AuCN value is usually suite of assays generally requested are: Ag.406 3. 2016). assay is a diagnostic test used for estimating the preg-robbing Mercury analysis. or carbonate carbon. near infrared/cation exchange where PRN = 0 indicates a nonpreg-robbing ore. represents inorganic carbon. germanium (Ge).4 g/t Au). in the presence of Au. Organic carbon subtracted from total carbon preparation protocol (Hanks and Barratt. calcium (Ca). The ICP/ICPMS actual deposit gold recovery.5 7. a second aqua-regia digestion carbon and/or clay content. Diagnostic leaching. Sulfide terization series of tests may include bond low energy impact. calculated International.625 30 15 7. sodium (Na). The organic carbon assay may also include nonpreg-robbing tests will affect the metallurgical study sample requirements and graphitic carbon. thorium (Th).5 is recoverable by cyanide leaching and is not a predictor of coupled plasma-mass spectrometry (ICPMS). potassium (K). petrography + AuCN (in g/t) (1) and optical microscopy. strontium (Sr). Diagnostic table can efficiently be measured with a four-acid digestion leach is a series of acid leaching. Diagnostic leaching is a protocol to Elemental analysis. primarily As.4 g/t Au (Au in the spike solution) diffraction (XRD). the carbon and sulfur contents of ores (LECO Corp.5 2.775 2. dried. 1986). 2000). kinetics. Armstrong and Malhotra. Minus 10 mesh bottle roll tests are 1992. After 48 or 96 hours. 24. once the cyanide for oxide gold ores concentration and grind particle size are optimized. conducted for at least 96 hours with recommended solution samples at 2. Leaching is usually conducted by applying passing 1. In addition and Huang. reagent cyanidation bottle roll leach tests should be conducted on master requirements and sensitivity to feed size under simulated heap composites as a function of crush size. sul. Lime will be added. For the milling process. equivalent to that with- are many test procedures available to evaluate the amenability drawn. such as the presence of coarse free gold content or 2. should be added to the pulps. generally 0. acetic acid. generally 80 percent leach conditions.0.and three-stage GRG test (Laplante. Woodcock cate to determine residual precious metal content.75 in. residues will be washed. 6. 48 and 72 hours to determine leach Gravity (coarse) gold determination. final pH and cyanide concentrations will be determined. Confirmation tests may be conducted at the NaCN concentration recommended Process development metallurgical studies for actual operation. milling processes or any combination of the roll cyanidation study to determine deposit-wide gold recovery leaching and milling processes. 2). The metallurgical program variations at the optimized condition. There adjusted as necessary.5 g NaCN per liter.7 mm (10 mesh Tyler). November 2016 • Vol. recovery rate. 8 and 24 hours. heap variability samples should be subjected to an agitated bottle or vat leaching. carbon-in-leach (CIL) or carbon-in-pulp (CIP) tests may be conducted for some ores. Kinetic mesh Tyler) to determine gold recovery. and 75 µm (200 mesh Tyler) cyanide solutions.5 the mineral matrix (Lorenzen. generally 80 percent passing 38 mm (1. Column per- process design criteria. hydrochloric acid and nitric acid are used either at and sensitivity to feed size. for oxide ores should therefore include dump/heap and vat leachability and milling studies (Fig.35 mm (6 Agitated bottle roll cyanidation leach studies. the pulps will be filtered and the • Screen fire assays. 8. reagent requirements furic acid.). when of a given sample to gravity gold recovery. 80 percent −200 mesh bottle roll tests are ery will be considered during project development for a number conducted for 48 hours with recommended solution samples at of reasons. 4.5 in. Leach • Small-scale batch gravity tests. 1995. to maintain the leaching pH at between 10. to kinetic leach tests.) and 3. In order to obtain the Column percolation cyanide leach studies.liberated from affected minerals. 33 No. over the Figure 2 — Oxide gold ores process development studies. 4 166 MINERALS & METALLURGICAL PROCESSING . In general. Similarly. 19 mm (0. 6. 4. Gravity gold recov. then the Gold may be extracted from oxide ores through dump. to determine gold recovery. recovery rate. and 11 adjusted with lime. the following tests are recommended colation leach tests should be conducted on master composite for oxide ores: samples as a function of crush size. Tumilty and Schmidt. Makeup water. weighed and assayed in tripli- • Single. The tests are usually conducted room temperature or at elevated temperature depending upon while maintaining 1 g/L NaCN and at pulp pH between 10. including: necessary.5 and 11. Cyanide concentration and pH should the potential opportunity to improve cash flow by producing be determined for each kinetic solution sample and will be a more readily saleable product early in the flow sheet. 33 No. for an industrial heap at the same crush size. charges at a rate of 10 L/hr/m2 of column cross-sectional area heap gold extractions. rule In order to determine dump leachability. the solution addition should be scaled 150 mm (6 in. pilot-scale column of thumb for cyanide consumption for an industrial heap with leach tests using columns with large diameters. For example. The data presented in these Figure 4 — Example of column leach gold extraction as a function of leach time for three crush sizes. should be conducted with 30-cm (12-in. The rule of thumb is to discount 3-5 respectively. 4 • November 2016 . Column leach gold extractions are also plotted as functions of leach time (Fig. MINERALS & METALLURGICAL PROCESSING 167 Vol. Figure 3 — Illustration of cyanide leach gold and silver extractions as functions of crush size. 4 and 5 indicate that gold extraction is roll and column leach tests should be plotted as functions of dependent on crush size and would be 55.) and 76 mm (3 in. Rule down by factoring in ore mass. from an industrial heap.) crush sizes. bulk sample or samples.). 42 and 17 percent for particle size (Fig. Fig. All columns should be leached of thumb would indicate using 48-50 percent gold extraction until extinction before being washed and taken offline. The The gold and silver extractions for the agitated bottle data illustrated in Figs. 3) to estimate gold and silver extractions 13 mm (0.) as-is or crushed consumption indicated by laboratory testing. considering the rule-of-thumb 5-percent deduc- percent from laboratory extractions when estimating industrial tion and solution-to-ore ratio of 1. 4) and solution-to-ore ratio (Fig. extraction for a primary crushed ore with 80 percent passing ference in column size. 5).) crush size would be about 53 percent. 25 mm (1 in. Similarly. usually 2 m or oxide ores would be to use about one-third of the cyanide 6 ft. Due to the dif. 3 indicates that gold for a 10-m lift height for an industrial heap.5 in. 20. cement or a combination while performing laboratory tests (Ellis and Senanayake. Some ores may contain cyanicides. for heap loading heights of 0. Therefore. and also the presence of clay concentration or oxygen levels were not maintained at the minerals. especially expansive clays. such as copper loading heights of up to 100 m. of lime and cement (Garcia and Jorgensen. special attention must smectite. 60. 2004). or slimes. The Cyanide concentration and pulp oxygen levels are other measured hydraulic conductivity rates will indicate if solution variables that should be considered during process development flow/percolation problems are anticipated for simulated heap studies. it will require considerable size reduction to obtain reasonable also called load-perm tests. Lower result of fine particles. Hydraulic conductivity tests. 1997).figures indicate that this ore type may not be heap leachable as Hydraulic conductivity tests. such as pyrrhotite. like montmorillonite and levels that the ore required. the ore be paid to the pulp cyanide concentration and oxygen level may require agglomeration with lime. Figure 6 — Generic heap leach metallurgical study flow sheet. assuming column leach residues to measure hydraulic conductivity rates it contains high enough gold grades. 40. should be conducted on select recoveries. 33 No. 80 and 100 m. It may be a good candidate for milling. 4 168 MINERALS & METALLURGICAL PROCESSING . In order to improve solution percolation rates. November 2016 • Vol. Solution flow problems are a minerals. or oxygen consumers. migrating to the lower por- gold extractions may be the outcome of testwork if the cyanide tions of the heap and blinding it. Figure 5 — Example of column leach gold extraction as a function of solution-to-ore ratio for three crush sizes. where x = 0 to 0. Things that could go wrong during process Process development metallurgical studies development studies for refractory gold ores Several things might go wrong in the course of conducting Refractory gold ore may be defined as an ore in which gold process development metallurgical studies. This paper will not go into the details of these individual some cases. in solid solution with sulfide tion of variability samples and master composites. Collins and Marczak. gold-containing 4. Gold may be very finely associated with the selection. and the selected variability sample Refractory gold ores require a pretreatment step. roasting — processes. drafting of minerals such as pyrite (FeS2). preparation and characteriza- disseminated in the ore matrix. resulting in a porous matrix domain: The master composite is prepared by combin- MINERALS & METALLURGICAL PROCESSING 169 Vol. Some examples of things that could go wrong and some and cyanicides such as copper sulfides. domain: A variability sample should represent a “met- 1995.. Simmons. 8. Master composite does not represent a metallurgical refractory minerals are oxidized. Wan and Brierley. In addition to hy- gravity-recoverable gold component. As a result. conducting of laboratory tests. preg-robbing carbonaceous ores. pyrrhotite [Fe(1 − x)S. and evaluating of and petzite (Ag3AuTe2). 1995. arsenopyrite (FeAsS) and ar. marcasite (FeS2 with precautions that should be taken are: orthorhombic crystal structure). allurgical response type. The metal- be fire-refined or reground and cyanide leached. During these processes. component be recovered by conducting gravity concentration blinding reagents such as kerosene or motor oil may be used for tests using instruments such as centrifugal gravity concentra. Figure 7 — Generic refractory ore metallurgical study flow sheet.” If the variability sample is a Brierley et al. These could be is resistant to leaching with cyanide. data granularity is lost.. A physical pretreatment option is ultrafine would be the mixing of refractory intercepts with an grinding of the ore to expose surfaces of finely disseminated oxide intercept. 2007. 4 • November 2016 . data for the metallurgical process selected. Gravity tails lurgical program for refractory ores should therefore include a may be cyanide leached to complete the material balance. If the ore has a coarse. flotation concentrates (Fig. 6. in order to render the gold leachable with 2. 1998. The choice of combination of 2-m intercept samples with significantly pretreatment option depends on the economics of the particular different cyanide-soluble gold to total gold ratios. In Fig. The gravity concentrate may are applicable to whole ore or flotation concentrates. or with naturally occurring 1. These pretreatment options tors. gold particles to cyanide leaching. physical or chemical. Pyke. 1997). for the cyanide to saturate and leach gold. pretreatment options study on the whole ore or gravity and/or A generic heap leach metallurgical study flow sheet is il. Gravity-recoverable gold studies. Variability sample does not represent a geometallurgical involves the oxidation of the gold-containing sulfide minerals domain: The variability sample is made out of several using hydrometallurgical — such as pressure or atmospheric lithologies and alterations and does not provide useful oxidation or biooxidation — or pyrometallurgical — that is. this ore type treated. which shows the major steps required to development metallurgical study options are summarized in develop an oxide gold deposit using a heap leach process. Sulfidic refractory ores process lustrated in Fig. Variability sample does not represent a mineable zone: carbonaceous preg-robbing material such as elemental carbon The mining method considered is openpit mining with or humic acids. a pilot column leach study using large-diameter processes and how development testwork should be conducted columns or demonstration heaps may be required to confirm for them. 10-m bench height. the results and analysis of smaller-scale tests. in the presence of oxygen consumers data. if selected. Chemical pretreatment 3. it is recommended that this drometallurgical and pyrometallurgical pretreatment processes. either is 25-30 m. 1999. the appropriate test program for the contemplated process or senian pyrite or telluride minerals such as calaverite (AuTe2) processes. Variability sample does not represent a metallurgical cyanide (Fernández. shaking tables and/or jigs. 33 No. Thomas et al.2)] and elemental sulfur. Johnston and Brooks. 7). November 2016 • Vol. Variability samples and master composites were prepared lurgical domains. combination of several variability samples irrespective lurgical domains. with incomplete characterization: Cyanide-soluble 6. 33 No. Master composite does not represent a given minable gold and preg-robbing gold assays along with sulfur horizon in the deposit: The master composite is a and carbon speciation are extremely important when Figure 8 — Sulfidic refractory gold ores process considerations. 7. several variability samples irrespective of geometal. ing several variability samples irrespective of metal. Master composite does not represent a geometallurgical of this is the combination of variability samples from domain: The master composite is a combination of different depths. and as a result data granularity is lost. 4 170 MINERALS & METALLURGICAL PROCESSING . An example 5. of where they are located in the deposit. .” The Second AUSIMM International the temperature at which sulfides are roasted must be Geometallurgy Conference.. pp. “Heap leach development . Australia.” Mineral Process- noncompliance and requirement for a costly new series ing Plant Design. Vol. No. “Can diagnostic leach procedures mance. 1986. 191-198. June 2. Inst. Peru.1016/j.doi.” MINDEV 97: The International Conference on Mine Project 12. pp. http://dx..” less steel mills may differ significantly. Society for Mining. A. Canada.. L. 15 Advances in Gold Ore Whincup. and Yeager.. Feb. P. Vina del system.L. 1992. Fleming. 1997. “The effects of dissolved oxygen and cyanide tention also needs to be paid to deleterious elements dosage on gold extraction from a pyrrhotite-rich ore. Metallurgy & References Exploration. Fernández. Woodcock. 33 No. J. K.. 119. 2009. biotreatment technology for processing lower grade refractory gold ores. C. 541-552.R. South Africa. 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No.E.J.F.. 1995. those achieved by the continuous pilot-plant autoclave. . Further reproduction prohibited without permission.Reproduced with permission of the copyright owner.