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Map showing the three cordilleras of the Northern Andes of Colombia. The Western Cordillera is on the left, then the Central in the middle, followed by the Eastern Cordillera on the right side. The La Colosa deposit is labelled with the red star. Original map provided by Sadalmelik, I. (2007).
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The goal of this project was to develop a predictive geometallurgical recovery model for the La Colosa porphyry gold deposit using the gold deportment, analytical data (multi-element assays), mineralogy, and recovery data. The aim of geometallurgy is to reduce risk and uncertainty by understanding the variability within the ore body, to increase th...
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Context 1
... La Colosa deposit lies on the eastern flank of the Central Cordillera and has a complex geologic history (Figure 3). Previous work on the regional geology of the area around La Colosa includes work by Goossens (1976); Sillitoe et al. (1982); Lozano (1984); Pulido (1988); Nunez (2001); Sillitoe (2007); Gil-Rodriguez (2010);and Lodder et al. (2010). ...
Context 3
... copper-gold deposits have a consistent suite of alteration assemblages. The alteration assemblages zone upward from sodic-calcic, deep in the base or roots of the porphyry system, to potassic, chlorite-sericite, sericite (phyllic), and advanced argillic at shallower levels ( Figure 33). The propylitic and chloritic alteration are zoned distally from the core. ...
Context 4
... advanced argillic alteration usually appears in the form of a lithocap, which may be up to 1 km thick (Sillitoe, 2010). The veinlets in porphyry deposits may be grouped into three general categories (their equivalents are listed by Gustafson and Hunt (1975) terminology): early quartz and sulfide-free veinlets (actinolite, magnetite (M type), early biotite (EB type) and potassic feldspar); granular quartz-dominated, sulfide-bearing with no alteration halos (A and B types); and crystalline quartz-sulfide veinlets and veinlets with feldspar destructive halos (D type) ( Figure 34). Potassic alteration is associated with the first two groups of veinlets. ...
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... of mineral associations observed with the gold-silver tellurides are shown in Figure 52. Gold-silver tellurides have an overall strong mineral association with apatite followed by albite and pyrite ( Figure 53 and Table 15). ...
Similar publications
The La Colosa, Colombia porphyry gold deposit is currently in the pre-feasibility stage. This large deposit has many types of gold mineralization: native gold, electrum, and tellurides. These variations in the gold mineralization lead to variability in the gold recovery. The final process flowsheet may include gravity concentration with cyanide lea...
The strategic mine plan is a crucial step for the success of mining companies, and for its development, it is necessary to use a number of inter-related variables that are usually estimated independently. These variables include operational data that is traditionally isolated in information islands between the different departments in the mine or t...
Citations
... Mineral Liberation Analyser, QEMSCAN, Mineralogic, TIMA-X), allow quantitative data on these characteristics to be acquired both quickly and relatively cheaply. Due to the wealth of information these techniques provide, they are commonly applied in geometallurgical studies Frenzel et al., 2018;Kern et al., 2018;Leichliter, 2013). They are also frequently used to numerically constrain the deportment of rare and precious metals (e.g. ...
Scanning electron microscope-based automated mineralogy studies are readily associated with quantitative results, providing one of the foundations of geometallurgical studies. Despite the importance of quantitative data for such studies, and efforts to reduce statistical errors, the reporting of uncertainties is rare. This contribution illustrates how bootstrap resampling can be used to provide robust estimates of statistical uncertainties for the modal mineralogy, metal deportment and all relevant textural attributes of a sample or a series of samples. Based on a case study of the Bolcana Au-Cu porphyry deposit in the South Apuseni Mountains, Romania, the impact of insufficient sampling statistics on quantitative mineralogical studies is illustrated. Quantitative analyses of the mineralogy and microfabric of milled ore samples from seven 40 m drill core intervals from the Bolcana Prospect were conducted using a Mineral Liberation Analyser (MLA), complemented by electron probe micro-analysis. Bootstrap resampling was then applied to assess how many grain mount surfaces should be analysed to achieve statistically robust results for both Cu and Au mineralogy, deportment and textural attributes. Despite variable mineralogy, grades and mineralisation styles, estimated statistical uncertainties on Cu deportment are consistently low. In contrast, uncertainties for Au deportment are so high that most reported values for important characteristics are statistically meaningless. This is mainly attributed to the pronounced nugget effect for Au mineralisation, exacerbated by the small sample size analysed by MLA. An unfeasible number of measurements would be necessary to provide robust figures for the deportment of minor/trace elements and minerals, along with other tangible mineralogical properties, such as mineral associations. The results of this case study demonstrate that statistical uncertainties need to be carefully incorporated when considering the results of automated mineralogical studies and their impact on geometallurgical models. This is particularly relevant for studies of precious metal ores.
... Mineral Liberation Analyser, QEMSCAN, Mineralogic, TIMA-X), allow quantitative data on these characteristics to be acquired both quickly and relatively cheaply. Due to the wealth of information these techniques provide, they are commonly applied in geometallurgical studies Frenzel et al., 2018;Kern et al., 2018;Leichliter, 2013). They are also frequently used to numerically constrain the deportment of rare and precious metals (e.g. ...
Scanning electron microscope-based automated mineralogy studies are readily associated with quantitative results, providing one of the foundations of geometallurgical studies. Despite the importance of quantitative data for such studies, and efforts to reduce statistical errors, the reporting of uncertainties is rare. This contribution illustrates how bootstrap resampling can be used to provide robust estimates of statistical uncertainties for the modal mineralogy, metal deportment and all relevant textural attributes of a sample or a series of samples. Based on a case study of the Bolcana Au-Cu porphyry deposit in the South Apuseni Mountains, Romania, the impact of insufficient sampling statistics on quantitative mineralogical studies is illustrated. Quantitative analyses of the mineralogy and microfabric of milled ore samples from seven 40 m drill core intervals from the Bolcana Prospect were conducted using a Mineral Liberation Analyser (MLA), complemented by electron probe micro-analysis. Bootstrap resampling was then applied to assess how many grain mount surfaces should be analysed to achieve statistically robust results for both Cu and Au mineralogy, deportment and textural attributes. Despite variable mineralogy, grades and mineralisation styles, estimated statistical uncertainties on Cu deportment are consistently low. In contrast, uncertainties for Au deportment are so high that most reported values for important characteristics are statistically meaningless. This is mainly attributed to the pronounced nugget effect for Au mineralisation, exacerbated by the small sample size analysed by MLA. An unfeasible number of measurements would be necessary to provide robust figures for the deportment of minor/trace elements and minerals, along with other tangible mineralogical properties, such as mineral associations. The results of this case study demonstrate that statistical uncertainties need to be carefully incorporated when considering the results of automated mineralogical studies and their impact on geometallurgical models. This is particularly relevant for studies of precious metal ores.
... No existe en la literatura gran información sobre aplicaciones de la geometalurgia a yacimientos de oro, muy probablemente debido a que un problema fundamental es el muestreo de este tipo de yacimientos (Pitard, 1989a y b;Goodall y Scales, 2007). Los trabajos más destacados con sistemas auríferos proceden de tesis desarrolladas en universidades australianas (Leichliter et al., 2011;Bonnici, 2012;Leichliter, 2013). El objeto del presente trabajo es el de dar a conocer los resultados más relevantes de un ensayo de modelo de recuperación geometalúrgica efectuado en la mina La Herradura en Sonora (Romero-Valle, 2017), una de las minas de oro más importantes de México, tomando en cuenta el análisis de la información obtenida a partir de estudios con microscopía de reflexión, concentración gravimétrica, Mineral Liberation Analyzer (MLA) y pruebas de cianuración dinámica. ...
La Herradura mine in Sonora is one of the most important gold districts in Mexico producing more than 5.5 million ounces of gold over 17 years. It is part of an orogenic gold deposits belt with a northwest-southeast direction for 300 km long and 50 kmwide. The mineralization consists of veins and quartz networks veinlets formed in a brittle-ductil geologic environment and it is hosted in Proterozoic quartz-feldspar gneisses. The ore bodies, defined by a 0.3 g/t Au cut-off grade, have tabular forms up to 1 km in length, 1 km in depth and 100 m in width. The visual control for mineralization is the abundance of quartz veins and veinlets, and a persistent sericitic hydrothermal alteration. Different techniques were used in this work with special focus on the Mineral Liberation Analizer (MLA) program to prove the possibility of predicting recoverable gold in the mine for the primary sulphide zone. Three geometallurgical zones (Zones A, B and C) were defined by ore composites and gravimetric concentrates from the same composites. Modal composition of the concentrates is quartz, feldspar and muscovite (sericite), and a metallic mineralogy of pyrite, sphalerite, galena, magnetite, gold and tellurides of gold and silver. Gold is identified as inclusions in pyrite or in gangue minerals like quartz, albite, orthoclase or ankerite, as well as coating pyrite crystals. The gold composition is electrum with 74 % Au and 26 % Ag; the presence of petzite (Ag3AuTe2) and stutzite (AgTe) were also identified. Recovery constants were calculated for each geometallurgical zone, which were introduced to the resource model of more than 14 million ounces of gold, indicating that error range in recoverable gold is less than 4 % for Zone A, 6 % for Zone C and 13 % for Zone B, in relation with gold recovery calculated with traditional methods. These results could be acceptable to applicate this methodology to La Herradura deposit. The most important error range in the Zone B is interpreted as due to a nugget effect, which isvery common in such mineral deposits. It is also concluded that the secondary milling process currently incorporated to the metallurgical plant is probably unnecessary, so its removal would result in a significant saving in energy and therefore in the economy of the mine.
... The gold mineralization at La Colosa consists of native gold, electrum, gold tellurides, gold-silver tellurides, and gold locked with sulfides (pyrite) Leichliter, 2012). Higher gold grades are also associated with a structure along the contact with the hornfels (host rock) which strikes northwest. ...
... Higher gold grades are also associated with a structure along the contact with the hornfels (host rock) which strikes northwest. The tellurides appear to concentrate near this same contact region, but are also found in all the major rock types Leichliter, 2012). ...
... Examples of mineral gold grains under the SEM(Leichliter, 2012).The gold telluride grains have an average grain size of 3 microns and are associated with K feldspar and pyrite with a majority liberatedLeichliter, 2012). A small amount of the gold telluride grains locked was in K feldspar and pyriteLeichliter, 2012).The gold-silver telluride grains have an average grain size of 2 microns and are found with apatite, albite, and pyrite. ...
The La Colosa, Colombia porphyry gold deposit is currently in the pre-feasibility stage. This large deposit has many types of gold mineralization: native gold, electrum, and tellurides. These variations in the gold mineralization lead to variability in the gold recovery. The final process flowsheet may include gravity concentration with cyanide leaching. Metallurgical testwork is utilized to identify the zones of ore that may be problematic to recover. To help select the samples that represent the fluctuating variability zones, geometallurgical models are constructed using mineralogy and geology data. These zones are then wireframed and compared to the geological and structural models for spatial correlation. Samples for the variability testwork will be selected from these different zones to identify and analyse the effect the different gold mineralization types have on the recovery. By using geometallurgy to aid in the sample selection for metallurgical testwork, the variability in the ore body can be understood and constrained to aid in process optimization.
... Metallurgical and geometallurgical studies on composited and selective samples indicate that gold occurs predominantly as native gold, as electrum, and in minor quantities as gold tellurides and gold-silver tellurides (Leichliter, 2013). Gold occurs as isolated grains and as inclusions or fracture fillings in pyrite, pyrrhotite, and silicate minerals such as feldspar and quartz (Fig. 12). ...
The La Colosa porphyry Au deposit is located on the eastern flank of the Central Cordillera of Colombia, within the Middle Cauca metallogenic belt. The deposit contains more than 800 t (22.37 Moz) Au at grades up to 0.8 g/t and is hosted by a composite porphyry stock of dioritic to tonalitic composition, which was emplaced into Triassic-Cretaceous schists of the Cajamarca Complex in the late Miocene (~8 Ma). The country rocks underwent two ductile deformation events, including development of shear zones, folds, and penetrative foliation, prior to emplacement of the stock. Subsequent brittle deformation reactivated preexisting N- and NNE-trending structures and formed secondary faults due to a change from right- to left-lateral shear sense on regional faults. This switch in stress orientations is attributed to a new plate configuration in the mid-Miocene. The left-lateral movement along regional faults favored emplacement of intrusive centers in dilational pull-apart zones, including the La Colosa stock within the regional Palestina fault zone. The La Colosa porphyry stock was intruded in three stages, termed early, intermineral, and late, all within a relatively short time interval of ~1.1 m.y. The early and intermineral stages are diorite porphyries and related intrusion breccias, whereas the late stage consists of quartz diorite and tonalite porphyries. The intrusions caused contact metamorphism and hydrothermal alteration that partially obliterated the original texture and composition of the schistose country rocks. The early and intermineral stages are dominated by potassic alteration, with local chloritic alteration in the core of the intermineral stage, sodic-calcic alteration in the deeper parts of the stock, and propylitic alteration confined to the late stage. Three gold mineralization events are recognized at La Colosa. The first was of porphyry style, during which hypersaline fluids (40-50 wt % NaCl equiv) formed predominantly A- and S-type veinlets and caused multistage wall-rock silicification accompanied by potassic and sodic-calcic alteration. The early-stage intrusions contain the highest gold grades varying from 0.75 to 1 g/t Au, associated with pyrite and minor chalcopyrite, molybdenite, and magnetite in the porphyries and with pyrrhotite-pyrite-melnikovite in the country rocks. In the intermineral-stage intrusions the gold grades drop to 0.5 to 0.75 g/t Au, and pyrrhotite and pyrite are the major sulfides. Gold grades reach low values of <0.3 g/t Au in the late-stage porphyries. The second gold-precipitating event formed sheeted veinlets of drusy quartz and pyrite with centimeter-wide halos of albite-sericite-pyrite overprinting all other alteration types at the deposit. A ~200°C hydrothermal brine (21-28 wt % NaCl equiv) deposited gold at high grades (>1.5 g/t Au over >10 m drill core intervals) within N-striking normal faults that developed during and after emplacement of the porphyry stock. The third mineralization event was supergene, with Au enrichment confined to late porphyries and characterized by sulfide boxworks, resulting in gold grade increases from 0.3 to 1.2 g/t Au. © 2018 Gold Open Access: this paper is published under the terms of the CC-BY-NC license.
With the increase in complexity of mineral deposits, understanding the grade variability is of high significance in getting enough information about the deposit, preventing financial losses and identifying optimized plans during and after exploitation. Likewise, mineralogical variability, grade, alteration … can highly effect metal recovery. Modeling these parameters is seriously substantial in order to have an optimized exploitation of the mine and to minimize the risks and costs. This study used the dataset of 91 drill holes from Sari Gunay epithermal gold deposit located in north-west of Iran to model gold grade and the recovery resulted from leaching tests. Initially, the oxide and sulphide zones were distinguished using Indicator Kriging and Simulation. Then the gold grade and recovery in each zone were modeled with the application of sequential Gaussian simulation and the developed block model. The grade-recovery curve was then drawn to estimate the total tonnage amount of the deposit which was related to the sulphide zone in more than 70%. Then with the help of recovery simulation data, the was considered a preferable parameter in depicting the curve and estimating the reserve.
The quantitative and qualitative assessment of gold grains from samples of glacial till is a well-established method for exploring gold deposits hidden under glaciated cover. This method, which is widely used in the industry and has resulted in numerous successes in locating gold deposits in glaciated terrain, is still based on artisanal gravity separation techniques and visual identification. However, being artisanal, it is limited by inconsistent recoveries and difficulties associated with visually identifying the predominantly small gold grains. These limitations hinder its capacity to decipher subtle or complex signals. To improve detection limits through the recovery of small gold grains, a new approach has recently been introduced into the industry, which is commercially referred to as the “ARTGold” procedure. This procedure involves the use of an optimized miniature sluice box coupled with an automated scanning electron microscopy routine. The capabilities of this improved method were highlighted in this study by comparing till surveys conducted around the Borden gold deposit (Ontario, Canada) using the conventional and improved methods at both local and regional scales. Relative to that with the conventional approach, the improved method increased the recovery of gold grains from samples (regional and down-ice mineralization) by almost one order of magnitude. (regional and down-ice mineralization), dominantly in regard of the small size fractions. Increasing the counts in low-abundance regional samples allows for a better discrimination between background signals and significant dispersions. The described method offers an alternative for improving the characterization of gold dispersal in glaciated terrain and related gold deposit footprints.
The Biely Vrch deposit in the Western Carpathians is assigned to the shallow, sulfide-poor porphyry gold deposit type and has an exceptionally low Cu/Au ratio. According to 3-D geochemical models, there is a limited spatial correlation between Au and Cu due to the primary introduction of gold by a salt melt and Cu by low-density vapor. Despite a rough spatial correlation of gold grades with quartz stockwork intensity, gold is hosted mostly by altered rock, exclusively in native form. Three main gold mineral assemblages were recognized here. In the deepest parts of the system, the K- and Ca-Na silicate gold assemblage is associated with minerals of high-temperature alteration (plagioclase, K-feldspar, actinolite), with gold grades and fineness depending on depth and potassium content of the host rock: K-silicate alteration hosts the lowest fineness gold (~ 914), whereas Ca–Na silicate alteration has the highest (~ 983). The intermediate argillic gold assemblage is the most widespread, with gold hosted mainly by chlorite, illite, smectite, and interstratified illite–chlorite–smectite minerals. The gold fineness is mostly variable (875–990) and inherited from the former gold mineral assemblages. The latest advanced argillic gold assemblage has its gold mostly in kaolinite. The extremely high fineness (~ 994) results from gold remobilization by late-stage aqueous magmatic-hydrothermal fluids. Uncommon bonanza-grade appears where the earlier gold mineral assemblages were further enriched by this remobilized gold. Primary precipitation of gold occurred during ascent and cooling of salt melts at 450 to 309 °C, mostly during retrograde quartz solubility.