Copper-gold Deposit Research Articles

Fluid Evolution of the Čukaru Peki Cu-Au Porphyry System (East Serbia) inferred from a fluid inclusion study

Čukaru Peki is a recently discovered copper-gold deposit in the Bor metallogenic zone in east Serbia. Three types of mineralization can be distinguished in this ore deposit: porphyry, high-sulphidation, and transitional epithermal type. This research was focused on fluid inclusion analysis of genetically different veins from the porphyry and the transitional zones of Čukaru Peki with an aim of better understanding the fluid evolution and mineralization processes in this system. Seven types of veins were identified in the porphyry zone of Čukaru Peki and four of these veins contained transparent minerals which were suitable for fluid inclusion analysis. Eight types of inclusion assemblages were distinguished in these veins: type 1 – primary inclusions with homogenization temperatures above 550°C and high salinity, type 2a- scattered polyphase inclusions two salt crystals, type 2b-polyphase inclusions with two salt crystals in crystal growth zones, type 3- brine inclusions with one salt crystal in crystal growth zones, type 4- vapour-rich inclusions, type 5- primary inclusions in anhydrite, and types 6 and 7- secondary low-temperature inclusions This research suggests that saline fluids (30-40% wt.% NaCl eq.) were the most important ones for the formation of porphyry-type mineralization and that the mineralization was formed at temperatures between 350 and 450°C and pressures between 100 and 500 bars. The epithermal stage was characterized by cooler low-salinity fluids with temperatures between 150-350°C, and salinity between 0 and 7 wt.% NaCl eq.

Mineralogical Setting of Precious Metals at the Assarel Porphyry Copper-Gold Deposit, Bulgaria, as Supporting Information for the Development of New Drill Core 3D XCT-XRF Scanning Technology

A petrographic investigation of ore samples from the Assarel porphyry copper deposit in the Srednogorie metallogenic zone (Bulgaria) constrains the setting and character of precious metals (Au, Ag, PGE) and related minerals within the deposit. This work supports renewed interest in understanding the deportment of precious metals and provides mineralogical knowledge during the testing and validation of novel drill core 3D X-ray computed tomography–X-ray fluorescence (XCT-XRF) scanning technology being developed as part of the X-MINE project. Scanning electron microscopy–energy dispersive spectrometry (SEM-EDS) results indicate precious metals occur in their native state (Au, Ag), as sulfides (Ag), sulfosalts (Au), tellurides (Ag, Pd), and selenides (Ag), and typically form micron-sized inclusions in pyrite and chalcopyrite or are disseminated in the groundmass of the rock. Preservation of early Fe oxide–chalcopyrite ± bornite assemblage as relics in the more dominant pyrite-chalcopyrite mineralization assemblage supports mineral disequilibrium relationships and multi-stage mineralization events. Several rare minerals (e.g., merenskyite, acanthite, sorosite, tetra-auricupride, auricupride, greenokite, bismuthinite, nagyagite, native Ni) are reported for the first time at Assarel and highlight the mineralogical diversity of the ore. The occurrence of precious metals and related minerals at Assarel attest to a complex hydrothermal system that underwent progressive physicochemical changes during the evolution of the mineralizing system (e.g., redox conditions, fluid chemistry).

Overprinting porphyry‐type veinlets on the intrusive rocks and phreatomagmatic breccias in the Southwest prospect, southwestern Sto. Tomas II (Philex), Baguio District, Philippines

AbstractThe Southwest prospect is located at the southwestern periphery of the Sto. Tomas II porphyry copper–gold deposit in the Baguio District, northwestern Luzon, Philippines. The Southwest prospect hosts a copper‐gold mineralization related to a complex of porphyry intrusions, breccia facies, and overlapping porphyry‐type veinlets emplaced within the basement Pugo metavolcanics rocks and conglomerates of the Zigzag Formation. The occurrences of porphyry‐type veinlets and potassic alteration hosted in the complex are thought to be indications of the presence of blind porphyry deposits within the Sto. Tomas II vicinity. The complex is composed of at least four broadly mineralogically similar dioritic intrusive rocks that vary in texture and alteration type and intensity. These intrusions were accompanied with at least five breccia facies that were formed by the explosive brecciation, induced by the magmatic–hydrothermal processes and phreatomagmatic activities during the emplacement of the various intrusions. Hydrothermal alteration assemblages consisting of potassic, chlorite–magnetite, propylitic and sericite–chlorite alteration, and contemporaneous veinlet types were developed on the host rocks. Elevated copper and gold grades correspond to (a) chalcopyrite–bornite assemblage in the potassic alteration in the syn‐mineralization early‐mineralization diorite (EMD) and contemporaneous veinlets and (b) chalcopyrite‐rich mineralization associated with the chalcopyrite–magnetite–chlorite–actinolite±sericite veinlets contemporaneous with the chlorite–magnetite alteration. Erratic remarkable concentrations of gold were also present in the late‐mineralization Late Diorite (LD). High XMg of calcic amphiboles (>0.60) in the intrusive rocks indicate that the magmas have been oxidizing since the early stages of crystallization, while a gap in the composition of Al between the rim and the cores of the calcic amphiboles in the EMD and LD indicate decompression at some point during the crystallization of these intrusive rocks. Fluid inclusion microthermometry suggests the trapping of immiscible fluids that formed the potassic alteration, associated ore mineralization, and sheeted quartz veinlets. The corresponding formation conditions of the shallower and deeper quartz veinlets were estimated at pressures of 50 and 30 MPa and temperatures of 554 and 436°C at depths of 1.9 and 1.1 km. Temperature data from the chlorite indicate that the chalcopyrite‐rich mineralization associated with the chlorite–magnetite alteration was formed at a much lower temperature (ca. 290°C) than the potassic alteration. Evidence from the vein offsetting matrix suggests multiple intrusions within the EMD, despite the K‐Ar ages of the potassic alteration in EMD and hornblende in the LD of about the same age at 3.5 ± 0.3 Ma. The K‐Ar age of the potassic alteration was likely to be thermally reset as a result of the overprinting hydrothermal alteration. The constrained K‐Ar ages also indicate earlier formed intrusive rocks in the Southwest prospect, possibly coeval to the earliest “dark diorite” intrusion in the Sto. Tomas II deposit. In addition, the range of δ34S of sulfide minerals from +1.8‰ to +5.1‰ in the Southwest prospect closely overlaps with the rest of the porphyry copper and epithermal deposits in the Sto. Tomas II deposit and its vicinity. This indicates that the sulfides may have formed from a homogeneous source of the porphyry copper deposits and epithermal deposits in the Sto. Tomas II orebody and its vicinity. The evidence presented in this work proves that the porphyry copper‐type veinlets and the adjacent potassic alteration in the Southwest prospect are formed earlier and at a shallower level in contrast with the other porphyry deposits in the Baguio District.

OPENING THE MAGMATIC-HYDROTHERMAL WINDOW: HIGH-PRECISION U-Pb GEOCHRONOLOGY OF THE MESOPROTEROZOIC OLYMPIC DAM Cu-U-Au-Ag DEPOSIT, SOUTH AUSTRALIA

Abstract Establishing timescales for iron oxide copper-gold (IOCG) deposit formation and the temporal relationships between ores and the magmatic rocks from which hydrothermal, metal-rich fluids are sourced is often dependent on low-precision data, particularly for deposits that formed during the Proterozoic. Unlike accessory minerals routinely used to track hydrothermal mineralization, iron oxides are dominant components of IOCG systems and are therefore pivotal to understanding deposit evolution. The presence of ubiquitous, magmatic-hydrothermal U-(Pb)-W-Sn-Mo–bearing zoned hematite resolves a range of geochronological issues concerning formation of the ~1.6 Ga Olympic Dam IOCG deposit, South Australia, at up to ~0.05% precision (207Pb/206Pb weighted mean; 2σ) using isotope dilution-thermal ionization mass spectrometry (ID-TIMS). Coupled with chemical abrasion-ID-TIMS zircon dates from host granite and volcanic rocks within and enclosing the ore-body, a confident magmatic-hydrothermal chronology is defined. The youngest zircon date from the granite intrusion hosting Olympic Dam indicates magmatism was occurring up until 1593.28 ± 0.26 Ma. The orebody was principally formed during a major mineralizing event following granite uplift and during cupola collapse, whereby the hematite with the oldest age is recorded in the outer shell of the deposit at 1591.27 ± 0.89 Ma, ~2 m.y. later than the youngest documented magmatic zircon. Hematite dates captured throughout major lithologies, different ore zones, and the ~2-km vertical extent of the deposit support ~2 m.y. of hydrothermal activity. New age constraints on the spatial-temporal evolution of the formation of Olympic Dam are considered with respect to a mantle to crustal continuum model. Cyclical tapping of magma reservoirs to maintain crystal mushes for extended time periods and incremental building of batholiths on the million-year scale prior to main mineralization pulses can explain the ~2-m.y. temporal window temporal window inferred from the data. Despite the challenge of reconciling such an extended window with contemporary models for porphyry deposits (≤1 m.y.), formation of Proterozoic ore deposits has been addressed at high-precision and supports the case that giant IOCG deposits may form over millions of years.

The influence of metal mobility on resource potential in circumneutral pH iron-rich copper mine waste rocks

Waste rocks from iron-oxide copper-gold (IOCG) deposits are dominated by Fe-bearing silicates and oxides, with only minor sulphides and potentially no pyrite. Hence, waste rock piles typically have circumneutral pH. However, oxidation of minor sulphides and Fe-bearing minerals can cause localised acidification at the mineral grain scale, especially where Fe oxidation and ferrihydrite precipitation is facilitated by bacteria. This study characterises the general biogeochemical system of waste rock piles at the Salobo IOCG mine, Brazil using a combination of biotic and abiotic leaching experiments on typical, weakly mineralised rocks, and observations of mineralogical changes and associated metal mobility in incipiently weathered, Cu-bearing overburden. Biotic experiments used a strain of the Fe- and S-oxidising Acidithiobacillus ferrooxidans subsp. cultured from the Salobo mine site. Most of the acid generated during oxidation of Salobo rocks is neutralised by alteration of labile Fe-silicates, particularly biotite, chlorite, olivine and amphiboles. Copper in our laboratory experiments was mobilised into solution (up to 1000 mg/l) from disseminated Cu-sulphide minerals during this acidification, and re-precipitated nearby (on the m-scale) within the rock mass during neutralisation. Much of this Cu precipitated with the abundant ferrihydrite, with some Cu precipitating locally with Mn-oxides, suggesting that secondary ferrihydrite and Mn-oxides represent possible exploration targets associated with comparable near-surface, weathered targets. Primary microparticulate gold was found encapsulated in magnetite and Cu-sulphides, with the sulphide-bearing portion of gold liberated during oxidation. Magnetite only demonstrated minor alteration (μm-scale) during short-term acidic oxidation (months). All these alteration processes are expected to occur within the waste piles during storage at the site, and could enhance the metallurgical leachability of these low-grade rocks for future re-processing. In the meantime, the lack of large-scale acidification, and adsorption of mobilised trace metals to the abundant ferrihydrite will ensure that the waste rocks remain environmentally benign.

Structural and non-structural statistical methods: implications for delineating geochemical anomalies

ABSTRACT Geochemical sampling media, be they rock chip, soil or stream sediment samples, routinely collected in mineral exploration, are key to detecting mineralisation-related geochemical dispersion patterns. Notwithstanding the diversity of methods applied to geochemical anomaly detection, they can be broadly divided into two major groups, namely structural and non-structural techniques. The former group covers those methods in which threshold values are assigned based on sample location while the sample locations are not required in the application of the non-structural techniques. In this study, rock chip samples from the Shadan porphyry copper–gold deposit are used to address the question as to how structural and non-structural methods can separate geochemical populations for the purpose of a deposit-scale study. It was revealed that the two structural techniques used in this study, concentration-area (C-A) fractal and U-spatial statistic methods, outperformed the non-structural techniques employed in this study.

The Varvarinskoye Complex Copper–Gold Deposit in Northern Kazakhstan: Mineral Types and Ore Composition

The Varvarinskoye copper–gold deposit, large in terms of Au and small in terms of Cu, was discovered in 1979 in the western part of the Torgai trough in Kazakhstan. It is composed of Devonian volcanosedimentary and intrusive rocks. Ore zones with a thickness from a few meters to a few tens of meters have been identified against a background of disseminated ore mineralization. They are composed of densely disseminated (porphyry) up to massive ores. The ore zones are localized in the thermal metamorphism band of volcanosedimentary and intrusive rocks, while disseminated mineralization is widespread beyond it. Ten ore mineralization types can be distinguished. The Au–Cu mineralization type is common in volcanosedimentary rocks and diorites, while the Au–Cu–Ni ores occur in serpentinites formed after thermally metamorphized intrusive rocks. Densely disseminated and massive magnetite ores are confined to skarns. Sulfide and sulfide–arsenide mineralization can also be observed. Each type of Au–Cu mineralization (pyrrhotite, chalcopyrite–marcasite–pyrite, pyrite, and gold–sulfide–arsenopyrite) can be correlated to an analog of Au–Cu–Ni mineralization (pentlandite–pyrrhotite, chalcopyrite–pentlandite–pyrite, pentlandite–pyrite, and gold–nickeline–gersdorffite). This indicates the uniform ore-forming process in serpentinites and volcanosedimentary rocks with diorites and borrowing of ore material from host rocks, at least, partially. The gold–chalcopyrite mineralization type, synchronous to the thermal metamorphism and analogous to mineralization of the alkali stage at porphyry copper deposits, has no analog in the Au–Cu–Ni mineralization. Gold is present in all mineralization types, but gold–chalcopyrite and sulfide–arsenide are the most enriched in Au. Eighty ore minerals have been found at the studied deposit. Pyrrhotite disulfidization and chalcopyrite pyritization are universal in occurrence. These processes likely led to the formation of chalcopyrite–marcasite–pyrite and chalcopyrite–pentlandite–pyrite mineralization after pyrrhotite and pentlandite–pyrrhotite types, respectively. Invisible gold present in chalcopyrite was enlarged during these processes.

Selective impurity removal and Cu upgrading of copper flotation concentrate by a spontaneously oxidative H2SO4 leaching process

The gradual decrease of global copper resources is among the most urgent challenges for the mining industry. Sustainable utilization of copper sulphide flotation concentrate from iron oxide copper gold (IOCG) deposits is often constrained by the impurity elements (e.g. U, Th and F) and high levels of gangue minerals (e.g. iron oxide/hematite, U-bearing minerals and fluorite). Herein, a spontaneous oxidative H2SO4 leach process (<100 °C) is proposed to selectively remove the penalty elements and upgrade copper sulphide concentrate from IOCG deposits. During H2SO4 leach, 87–92% of F element in the fluorite mineral was extracted and the dissolution of iron oxide/hematite minerals were enhanced by the elevated temperature at 60–90 °C. The released Fe3+ ions from iron oxide/hematite minerals worked as the spontaneous oxidant for dissolving U-bearing minerals and upgrading copper minerals. The results reveal that the H2SO4 leach in presence of dissolved Fe3+ effectively removed 88–97% U and 89–90% Th from U-bearing minerals. Meanwhile, the elevated temperature at 60–90 °C plays a critical role in the phase transformation of bornite to covellite in the presence of Fe3+. Another phase transformation of chalcopyrite to bornite was also significant at the higher temperature of 90 °C through the non-oxidative dissolution mechanism. During the spontaneous oxidative H2SO4 leach, the dissolution of gangue minerals and phase transformations of copper minerals successfully upgraded copper concentrate from 41.1 to 50.5 wt% at 90 °C, while copper dissolution was maintained at less than 7.7%.

Textures and geochemistry of magnetite: Indications for genesis of the Late Paleozoic Laoshankou Fe-Cu-Au deposit, NW China

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and electron probe X-ray microanalysis (EPMA) have been employed to determine major and trace elemental concentrations in magnetite from different ores in the Laoshankou deposit, which is the most important Fe-Cu-Au deposit in the northern margin of East Junggar. Two magnetite-associated paragenetic sequences have been defined in Laoshankou, including amphibole-epidote-magnetite alteration/mineralization (stage II) and pyrite-chalcopyrite mineralization (stage III-B). On the basis of the magnetite textures and chemical compositions, we have identified six generations of magnetite from three types of ores/rocks, including the high-Ti inclusion-rich M-1-A and inclusion-free M-1-B in massive magnetite-epidote-amphibole ores (type H1) from stage II; the low-Ti, high-Si, inclusion-rich M-1-C in massive magnetite-sulfide ores (type H2) from stage II; the ubiquitous low-Ti M-2 and pristine low-Ti, low-Si M-3 in both H1 and H2 types; and M-4 within massive chalcopyrite-magnetite ores (type H3) from stage III-B. The discriminations of V versus Ti, Ca + Mn + Al versus Ti + V, and Fe versus V/Ti, as well as mineral assemblages and trace element concentrations of Cr (<1000 ppm) and V (<300 ppm), collectively imply that all the generations of magnetite are hydrothermal in origin, and more likely similar to those in iron-oxide copper-gold deposits. The diverse textural and chemical features among these generations of magnetite indicate that they have formed from distinct process. The earliest M-1-A and M-1-B in type H1 ore and M-1-C in type H2 ore were replaced by M-2 along fractures and/or grain boundaries of the M-1-A/B/C, forming a number of mineral inclusions via dissolution and reprecipitation. Following this, M-3 veins generally crosscut all of these above types. Finally, high-Co, Ni, and REE-rich fluid formed the chalcopyrite-associated M-4 with dark-light zoning in the type H3 ore from pyrite-chalcopyrite mineralization. These elevated lithophile (REE) and chalcophile (Co, Ni) elements within the chalcopyrite (sulfide)-associated M-4 further suggest that non-magmatic fluid dominated in the fluid system, with intensive fluid-rock interactions and low-temperature, Cl, and Cu-rich external fluid accounting for the Cu-Au mineralization.

Experimental simulations of bacterially-mediated magnetite oxidation and observations on ferricrete formation at the Salobo IOCG mine, Brazil

Previous data provides evidence that magnetite-rich rock material can sustain large populations of acidophilic, iron-oxidising bacteria. Here we investigate the role of microbially-mediated oxidation of magnetite in more detail, using a strain of Acidithiobacillus ferrooxidans cultured from weathered, iron-rich rocks at the Salobo iron-ore copper-gold (IOCG) deposit, Brazil. The bacterially-mediated oxidation experiments provide evidence for bacterial colonisation and biogeochemical interaction with magnetite mineral surfaces. Experiments were run with different substrates and varying geochemical conditions in three laboratory scenarios: (1) Oxidation of ultrafine chemical grade nano-particulate magnetite over 60 days; (2) oxidation of near-pure magnetite blocks over 90 days; and (3) oxidation of magnetite-rich ore over 180 days. Attachment strategies of bacterial cells to mineral substrates varied with substrate, pH and availability of ferrous iron in solution; colonisation of minerals was generally non-selective. Under acidic conditions (pH 2–3), magnetite oxidation was driven by chemical dissolution that caused crystallographically-controlled differential corrosion of mineral surfaces. At pH > 4, iron-oxidising bacteria that attached to magnetite surfaces did not cause visible surface changes, and we infer that magnetite oxidation may have been occurring via internal electron diffusion, forming pseudomorphous maghemite. The activity of acidophilic bacteria can create local acidic microenvironments in ambient circumneutral pH settings, especially on Fe2+-bearing silicates and sulphides that accompany magnetite. These microenvironments can affect magnetite bio-oxidation mechanisms, causing some magnetite dissolution and/or alteration. Bacterially-oxidised ferric iron, derived from dissolution of magnetite and associated minerals, is precipitated as ferric (oxyhydr)oxide at circumneutral pH. We compare the results of these laboratory studies to observations on magnetite alteration textures in ferricrete overlaying the ore body at the Salobo mine. We suggest that magnetite is also bioavailable to iron-oxidising bacteria in other surficial, acidic to circumneutral pH settings, such as mine tailings and can contribute to varying alteration and dissolution/precipitation processes involving magnetite.

Evolution of brines and CO2-rich fluids and hydrothermal overprinting in the genesis of the Borrachudo copper deposit, Carajás Province

The Carajás Province is one of the world’s major domains of iron oxide-copper-gold (IOCG) deposits, which formed during the Neoarchean (ca. 2.70–2.68 Ga and ca. 2.57 Ga). The province also hosts other copper-gold deposits of Paleoproterozoic age (ca. 1.88 Ga). The Borrachudo copper deposit is located about 6 km southwest of the world-class Cristalino IOCG deposit. Porphyritic rhyolite and amygdaloidal andesite of the ca. 2.76–2.74 Ga Grão Pará Group, formed in a volcano-plutonic event during the Neoarchean, are the main host to the Borrachudo deposit. Copper mineralization was related to two distinct hydrothermal events. The first, controlled by the development of ductile structures, was likely linked to the Carajás ca. 2.70 Ga IOCG system. It evolved from sodic alteration, silicification, and iron metasomatism through to calcic and potassic alteration. Chalcopyrite strings along foliation, breccias, and massive ore represent early copper mineralization. During the early hydrothermal event, aqueous (165° to >400 °C; 0.23 to >38.32 wt% NaCl equiv.), aqueous-carbonic and carbonic fluid inclusions (TmCO2 = −60.1 to −59.4 °C; CO2 density of 0.82 to 0.97 g/cm3) were trapped in quartz formed during the silicification. Immiscibility of a magmatic fluid or heterogeneous trapping of brines and CO2-bearing fluids, followed by mixing with diluted colder fluids, are suggested. The late event, controlled by brittle structures, records recurrence of hydrothermal alteration stages, such as silicification, sodic alteration, and potassic alteration, as well as chlorite and carbonate alteration. The copper mineralization is represented by chalcopyrite in branched breccia pipes and veins with minor magnetite, pyrite, siegenite, cobaltite, galena, anglesite, uraninite, and thorite. Titanite in veins of albite-chalcopyrite-apatite yielded an LA-ICP-MS U-Pb titanite age of 2011 ± 6.8 Ma. During the late hydrothermal event, aqueous fluids (140 to >320 °C; 6.7 to 40 wt% NaCl equiv.) reflected a more advanced mixing process involving diluted external fluids. The Borrachudo deposit points to the recurrence of multiple hydrothermal events responsible for the copper metallogenesis, which were intrinsically controlled by the magmatic and tectonic evolution of the Carajás Province.

Geological, mineralogical, and oxygen isotope studies of the Chandmani Uul iron oxide–copper–gold deposit in Dornogobi Province, Southeastern Mongolia

AbstractThe Chandmani Uul deposit is located in Dornogovi province, Southeastern Mongolia. Iron oxide ores are hosted in the andesitic rocks of the Shar Zeeg Formation of Neoproterozoic to Lower‐Cambrian age. Middle‐ to Upper‐Cambrian bodies of granitic rocks have intruded into the host rocks in the western and southern regions of the deposit. The wall rocks around the iron oxide ore bodies were hydrothermally altered to form potassic, epidote, and sericite–chlorite alteration zones, and calcite and quartz veinlets are ubiquitous in the late stage. Since granitic rocks also underwent potassic alteration, the activity of the granitic rocks must have a genetic relation to the ore deposit. The ore mineral assemblage is dominated by iron oxides such as mushketovite, euhedral magnetite with concentric and/or oscillatory zoning textures, and cauliflower magnetite. Lesser amounts of chalcopyrite and pyrite accompany the iron oxides. Among all these products, mushketovite is dominant and is distributed throughout the deposit. Meanwhile, euhedral magnetite appears in limited amounts at relatively shallow levels in the deposit. By contrast, cauliflower magnetite appears locally in the deeper parts of the deposit, and is associated with green‐colored garnet and calcite. Sulfide minerals are ubiquitously associated with these iron oxides. The oxygen isotope (δ18O) values of all types of magnetite, quartz, and epidote were found to be −5.9 to −2.8‰, 10.5 to 14.9‰, and 3.6 to 6.6‰, respectively. The δ18O values of quartz–magnetite pairs suggest an equilibrium isotopic temperature near 300°C. The calculated values of δ18O for the water responsible for magnetite ranged from 2 to 10‰. All the data obtained in this study suggest that the iron oxide deposit at the Chandmani Uul is a typical iron oxide–copper–gold deposit, and that this deposit was formed at an intermediate depth with potassic and sericite–chlorite alteration zones under the oxidized conditions of a hematite‐stable environment. The δ18O range estimated implies that the ore‐forming fluid was supplied by a crystallizing granodioritic magma exsolving fluids at depth with a significant contribution of meteoric water.

Breccia, hydrothermal alteration and structural geology of the Huangtun porphyry Au-Cu deposit in the Middle-Lower Yangtze Metallogenic Belt, eastern China

Luzong Basin is an important part of the Middle-Lower Yangtze Metallogenic Belt in eastern China, in which the dominant types of deposits are iron-oxide-apatite and skarn iron deposits. However, a new porphyry gold-copper deposit, Huangtun deposit, has recently been discovered in the north-eastern margin of the basin. Detailed studies of geological characteristics and metallogenic processes of Huangtun gold-copper deposit are needed to supplement the mineralisation type of the Luzong Basin. Based on drill core logging and petrology observations of thin sections and polished sections, a north-striking sinistrial strike-slip major fault and a series of secondary NE-striking sinistrial strike-slip faults have been identified in the mining area. A mineralised breccia pipe at the intersection of the two groups of faults is the main host of the Au ore body. The alteration types in the mining area, from deep to shallow, include an albite alteration zone, a biotite-albite alteration zone, a chlorite alteration zone and a sericite-pyrite alteration zone. A detailed mapping of the breccia pipe has been provided in the mining area. Seven different breccias facies have been divided according to the internal structure, composition, morphology, matrix content and alteration assemblages. Genesis of the different breccia facies have been identified based on crosscutting relationships and clast-in-clast textures, which revealed that there are two different faulting and brecciation stages. During the first stage, matrix-supported breccia formed near the fracture zone. Gold-copper mineralisation then occurred along the intersection of the two groups of fracture zones, which formed K-Na silicate to sericite altered magmatic-hydrothermal breccia, from deep to shallow. In addition, these different facies of breccia correspond to four stages of fluid evolution: the albite stage, biotite-albite stage, chlorite stage and sericite-pyrite stage. Hydrothermal breccia with a high matrix/cement ratio then formed when mineralizing fluid permeated the fracture zone. During the second stage, the ore bodies were faulted to form tectonic breccia containing some massive carbonate ± quartz ± pyrite clusters as clasts. Based on the current study, we conclude that the locations of the intersection of fault zones in the northern part of the Luzong Basin and the northern part of the mining area have potential for further gold mineralisation.

Mineralization parameters and exploration targeting for gold – copper deposits in the Baguio (Luzon) and Pacific Cordillera (Mindanao) Mineral Districts, Philippines: A review

The Baguio Mineral District in Luzon, Philippines is known to host several world-class epithermal gold – porphyry copper deposits. The interplay of tectonic setting, magma composition, structural control and hydrothermal systems contributed to the generation of these deposits. Ridge subduction (Scarborough seamount) resulting to flat subduction and a transpressional regime could also be related to the formation of epithermal gold - porphyry copper deposits in Baguio. Subduction processes leading to the formation of calc-alkaline rocks associated with high water pressure, oxygen fugacity and late sulfur saturation are almost always associated with the gold-copper deposits in the district. Compared to the Baguio Mineral District, less exploration work, mine development and production were done in the Pacific Cordillera Mineral District, Mindanao in southern Philippines. It is worth noting, however, that both mineral districts show similarities and overlapping features in terms of geological, geophysical and geochemical characteristics. This leads one to conclude that the Pacific Cordillera Mineral District has ore deposits waiting to be discovered.

Prospects for using combined (traditional and physical-chemical) mining technologies in the development of large gold-copper ore deposits

The article deals with the problems of development of large gold-copper ore deposits, which have prospects for the development of mining and processing complexes based on them, which produce refined metals as final products. The article substantiates the feasibility of using combined traditional and physical-chemical geotechnologies in the development of these deposits, including geotechnologies in mining, using innovative processes of activation of heap and underground leaching of copper, fine and dispersed gold from complex ores. At the initial stage of development of the large deposits of complex ores, in parallel with traditional schemes open-pit mining and ore processing at the processing plant, it is advisable to use the activation heap leaching of valuable components from poor and refractory ores and flotation tailings from ordinary and rich ore. At the second stage, when switching to the underground method of field development, it is proposed to use blockhole leaching with explosion-injection ore preparation with combination with it. The proposed schemes for combined development of complex gold-copper ore and copper-ore deposits with precious metal mineralization are based on data obtained during many years of experimental research and pilot tests.

Mineralization signatures of the magnetite-dominant Acropolis prospect, Olympic Dam IOCG district, South Australia

The Acropolis prospect is a vein-style magnetite (±apatite ±hematite) system located ~20 km southwest from the giant Olympic Dam iron-oxide copper gold (IOCG) deposit, South Australia. A whole rock...

Mapping IOCG-related alteration using 3D gravity and magnetic inversion: an example from the Tennant Creek – Mount Isa region, northern Australia

To support the Exploring for the Future (EFTF) initiative, identification of possible hydrothermal alteration systems associated with iron oxide copper-gold (IOCG) deposits has been carried out in ...

Structural controls of the Ernest Henry IOCG deposit: Insights from integrated structural, geophysical and mineralogical analyses.

Iron Oxide Copper-Gold deposits (IOCGs) are structurally controlled, and typically display zonation of iron oxides and sulphides, which is potentially related to redox zonation. There are three mai...

Bacterially-mediated supergene alteration and redistribution of copper in mineralised rocks at the Salobo IOCG deposit, Brazil

The primary ore at the giant Salobo iron oxide copper-gold (IOCG) deposit in Brazil is dominated by magnetite and Fe-rich silicates, with minor (~1%) disseminated Cu-Fe sulphides and a distinctive absence of pyrite. Supergene Fe-silicate and sulphide oxidation has been mediated by bacteria, commonly within micrometre-scale acidic environments, but silicate-dominated acid neutralisation has maintained ambient circumneutral pH. Supergene Cu mobility has been controlled by the highly localised Fe-dominated biogeochemical processes, with Cu redistribution on the micrometre to metre scales and negligible supergene Cu enrichment. Silicates, especially the phyllosilicates biotite and chlorite, have variably altered to the clay minerals vermiculite and/or smectite, and ultimately to kaolinite. Leaching of Mn, Fe, Mg and Si accompanied silicate alteration, with minor addition of Cu to clay mineral structures and along cleavage planes. Iron mobilised by bacterial oxidation processes initially precipitated as ferrihydrite (with up to ~10 wt% Cu). Most Cu and Mn, mobilised in localised acidic environments, were precipitated nearby (metre scale) at circumneutral pH and reflect the immediate supergene biogeochemical environments: Cu-carbonates, pseudomalachite, chrysocolla, and Cu-Mn oxides (= “copper wad”). The early stages of these natural supergene processes were simulated in laboratory leaching studies using a range of fresh rocks inoculated with an endemic iron-oxidising strain of Acidithiobacillus ferrooxidans previously cultured from the Salobo site. Bacterially-mediated precipitation of ferrihydrite, commonly Cu-bearing, in these experiments strongly resembles that seen in the natural outcrops. These leaching experiments confirmed the effectiveness of silicate-dominated acid neutralisation, especially when accompanied by bornite oxidation, which is also acid-consuming. In contrast, chalcopyrite oxidation is acid-producing and leads to more effective localised Cu mobility in solution. Our combination of field and laboratory observations at the Salobo IOCG deposit shows that the biogeochemical environment dominated by Fe-silicates with little sulphides, typical for these systems, has led to an entirely different style of supergene Cu redistribution from that seen at many other Cu deposits, such as chalcopyrite and pyrite-rich porphyry copper deposits, where substantial supergene Cu enrichment has occurred.

Delineation of alteration zones based on artificial neural networks and concentration-volume fractal methods in the hypogene zone of porphyry copper-gold deposit, Masjed-Daghi, East Azerbaijan Province, Iran

In this paper, we aim to achieve two specific objectives. The first one is to examine the applicability of the Artificial Neural Networks (ANNs) technique in ore grade estimation. Different training algorithms and numbers of hidden neurons are applied to estimate Cu grade of borehole data in the hypogene zone of porphyry copper-gold deposit, Masjed-Daghi, East Azerbaijan Province (Iran). The efficacy of ANNs in function-learning and estimation is compared with ordinary kriging (OK). As the kriging algorithms smooth the data, their applicability in the pre-processing of data for fractal analysis is not conducive. ANNs can be introduced as an alternative for this kind of problem. Secondly, we aim to delineate the potassic and phyllic alteration regions in the hypogene zone of Cu-Au porphyry deposit based on the estimation obtained by the ANNs and OK methods, and utilize the Concentration-Volume (C-V) fractal model. In this regard, at first, C-V log-log is generated based on the ANN results. The plots are then used to determine the Cu threshold values for the alteration zones. To investigate the correlation between the geological model and C-V fractal results, the log ratio matrix is applied. The results obtained show that Cu values less than 0.38% from ANNs have more overlapped voxels with phyllic alteration zone by an overall accuracy of 0.72. Spatial correlation between the potassic alteration zones resulting from 3D geological modeling and high concentration zones in C-V fractal model show that Cu values greater than 0.38% have more voxels overlapped with the potassic alteration zone by an overall accuracy of 0.76. Generally, the results obtained show that a combination of the ANNs and C-V fractal methods can be a suitable and robust tool for quantitative modeling of alteration zones instead of the qualitative methods.