Giant Gold Deposit Research Articles

Carbonate metasomatism in the lithospheric mantle: Implications for cratonic destruction in North China

The activity of melts and fluids may have played a key role in inducing the destruction of the eastern North China Craton in the early Cretaceous. Carbonate melts are important agents in mantle metasomatism and can significantly modify the physical and chemical properties of the subcontinental lithospheric mantle. Carbonate metasomatism can be identified by specific geochemical indices in clinopyroxene, such as high Ca/Al and low Ti/Eu ratios. This study presents the spatial and temporal variations of carbonate metasomatism in the lithospheric mantle beneath the eastern North China Craton. Three types of carbonate metasomatism are classified based on the geochemical compositions of clinopyroxene in mantle peridotites. Clinopyroxene formed by Type 1 carbonate metasomatism is characterized by very high Ca/Al ratios (15–70) and 87Sr/86Sr ratios (0.706–0.713). Clinopyroxene derived from Type 2 carbonate metasomatism shows relatively high Ca/Al ratios (5–18) and 87Sr/86Sr ratios (0.703–0.706). However, clinopyroxene resulting from Type 3 carbonate metasomatism has low Ca/Al ratios (5–9) and 87Sr/86Sr ratios (0.702–0.704). Deep (garnet-bearing) and shallow (spinel-bearing) lithospheric mantle beneath the Sulu orogen and surrounding areas in the eastern North China Craton were affected by intense Type 1 carbonate metasomatism before the late Triassic. The deep subduction of the South China Block with its accompanying carbonate sediments was the trigger for Type 1 carbonate metasomatism, which reduced strength of the lithospheric mantle and provided a prerequisite for the destruction of the eastern North China Craton in the early Cretaceous. After the destruction of the eastern North China Craton, the ancient relict lithospheric mantle, represented by spinel harzburgite xenoliths hosted in the late Cretaceous to Cenozoic basalts, only recorded Type 2 carbonate metasomatism. This implies that the lithospheric mantle experienced the intense Type 1 carbonate metasomatism was completely destroyed and not preserved during decratonization. Spinel lherzolite xenoliths hosted in the late Cretaceous to Cenozoic basalts represent the young, fertile lithospheric mantle formed after the cratonic destruction and only a few samples record Type 2 and 3 carbonate metasomatisms. We suggest that carbonate melts derived from the subduction-modified asthenospheric mantle with variable proportions of recycled crustal material was responsible for the Type 2 and 3 carbonate metasomatisms. The carbonate metasomatism of the lithospheric mantle beneath the Jiaodong Peninsula and surrounding areas is very pervasive and is spatially consistent with the remarkable thinning of lithospheric mantle and giant gold deposits in this region. Therefore, we conclude that carbonate metasomatism in the lithospheric mantle played a crucial part in the modification, destruction and gold deposits in the eastern North China Craton.

Unusual Quartz Phenocrysts in a Newly Discovered Porphyritic Granite near the Giant Dongping Gold Deposit in Northern Hebei Province, China

Unusual Quartz Phenocrysts in a Newly Discovered Porphyritic Granite near the Giant Dongping Gold Deposit in Northern Hebei Province, China

Decratonic gold mineralization: Evidence from the Shangzhuang gold deposit, eastern North China Craton

The Jiaodong Peninsula in the eastern North China Craton (NCC) hosts some of the world-class gold deposits. Among these, the Shangzhuang gold deposit represents a typical fault-zone hosted disseminated- and stockwork-style gold mineralization. The mineralization is characterized by intense hydrothermal alteration halos in the wallrocks with the mineralized veins intruding into altered wallrocks. Zircon U-Pb isotope dating constrains the timing of emplacement of the Guojialing granodiorite as 130±1Ma. Five molybdenite samples from the main mineralization stage veins yielded a well-fitted isochron age of 126±2Ma (MSWD=1.3), marking the timing of gold mineralization. Four types of fluid inclusions are identified at Shangzhuang, and their petrographic and microthermometric features suggest fluid immiscibility followed by fluid mixing. This inference is also supported by oxygen and hydrogen isotopic data of quartz veins from stage III. The measured δ18O values of quartz are +12.3 to +13.7‰ for stage II and +11.7 to +12.0‰ for stage III, with calculated δ18Ofluid values for stage II ranging from +5.9 to +7.3‰ and for stage III from +3.4 to +3.7‰. δD values for stage II and III quartz range from −65.3 to −75.2‰ and −70.6 to −74.7‰, respectively. The data suggest that the ore-forming fluids were initially derived from magmatic sources, followed by mixing with meteoric water. SIMS in-situ sulfur isotope analyses of two types of pyrite (Py I and Py II) from different mineralization stages show different sulfur isotope features. The δ34S values for Py I (+10.2 to +11.3‰, mean=+10.8‰, n=25) are higher than those of the later mostly gold-related Py II (+4.1 to +6.8‰, mean=+5.4‰, n=27). The higher δ34S values of Py I are correlated to degassing of mantle wedge metasomatized by the slab fluids. The relatively lower δ34S values of Py II might suggest increasing of fO2 through fluid mixing between ore-forming fluids and meteoric water.The temporal, spatial and tectonic relations between the giant gold mineralization and destruction of the NCC suggest a genetic linkage. The gold mineralization between 126 and 117Ma at Jiaodong was probably initiated at the peak of decratonization (ca. 125Ma) of the eastern NCC. Phanerozoic craton margin orogeny also played a critical role in the generation of the early Cretaceous giant gold deposits in the eastern NCC. Integrated geological characteristics, mineralization features, metallogenic age, sources of ore-forming fluids and sulfur, and tectonic settings favor a decratonic gold mineralization model for the Shangzhuang gold deposit. The geodynamic scenario proposed for the early Cretaceous giant gold mineralization event in the eastern NCC includes the paleo-West Pacific plate subduction, asthenospheric upwelling, multiple subduction-collision processes along the margins.

Plume-subduction interaction forms large auriferous provinces

Gold enrichment at the crustal or mantle source has been proposed as a key ingredient in the production of giant gold deposits and districts. However, the lithospheric-scale processes controlling gold endowment in a given metallogenic province remain unclear. Here we provide the first direct evidence of native gold in the mantle beneath the Deseado Massif in Patagonia that links an enriched mantle source to the occurrence of a large auriferous province in the overlying crust. A precursor stage of mantle refertilisation by plume-derived melts generated a gold-rich mantle source during the Early Jurassic. The interplay of this enriched mantle domain and subduction-related fluids released during the Middle-Late Jurassic resulted in optimal conditions to produce the ore-forming magmas that generated the gold deposits. Our study highlights that refertilisation of the subcontinental lithospheric mantle is a key factor in forming large metallogenic provinces in the Earth’s crust, thus providing an alternative view to current crust-related enrichment models.

The golden ark: arsenopyrite crystal plasticity and the retention of gold through high strain and metamorphism

AbstractQuantitative electron backscatter diffraction analysis and ion microprobe imaging of gold‐rich arsenopyrites provide the first insights into the crystal plasticity and element mobility behaviour of arsenopyrites through metamorphism (340°–460° and 2 kbar). Remarkably, the gold‐rich arsenopyrites remained structurally and chemically robust during high strain deformation. It was only during a superimposed lower strain deformation event, at a high angle to the preferred orientation of the arsenopyrites, that small amounts of crystal plasticity affected the arsenopyrites. During the low strain event, a dissolution–reprecipitation reaction resulted in loss of gold from the crystal lattice, facilitated by localised domains of recrystallisation, most likely due to fluid percolation along sub‐ and new grain boundaries. We suggest that the abundance and rheologically robust nature of gold‐rich arsenopyrite in giant gold deposits, affected by greenschist–amphibolite metamorphism, is actually critical in the preservation of those deposits.

The conjunction of factors that lead to formation of giant gold provinces and deposits in non-arc settings

It is quite evident that it is not anomalous metal transport, nor unique depositional conditions, nor any single factor at the deposit scale, that dictates whether a mineral deposit becomes a giant or not. A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc environments. For giant orogenic, intrusion-related gold systems (IRGS) and Carlin-type gold deposits and iron oxide-copper-gold (IOCG) deposits, there are common factors among all of these at the lithospheric to crustal scale. All are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or, in the case of most Phanerozoic orogenic giants, define the primary suture zones between tectonic terranes. Giant provinces of IRGS, IOCG, and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant province. The IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids, whereas the association of such melts with Carlin-type ores is more indirect and enigmatic. Giant orogenic gold provinces show no direct relationship to such magmatism, forming from metamorphic fluids, but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order structures.In contrast to their province scale similarities, the different giant gold deposit styles show contrasting critical controls at the district to deposit scale. For orogenic gold deposits, the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits, with resultant geometrical and lithostratigraphic complexity as a guide to their location. There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits, and those few giants are essentially preservational exceptions. Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks, enriched in syngenetic gold, to be located below an impermeable cap along antiformal “trends”. Hydrocarbons probably played an important role in concentrating metal. The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock. All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources, partly due to economic factors for this relatively poorly understood, low Cu-Au grade deposit type. The supergiant Olympic Dam deposit, the most shallowly formed deposit among the larger IOCGs, probably owes its origin to eruption of volatile-rich hybrid magma at surface, with formation of a large maar and intense and widespread brecciation, alteration and Cu-Au-U deposition in a huge rock volume.

A Preliminary Review of Metallogenic Regularity of Gold Deposits in China

AbstractGold is one of the most important mineral resources in China with its rich mineral resources. In recent years, significant progress has been made on the process of gold resource exploration. Some large and giant gold deposits were newly found and some important expansions in the main mining regions were also been completed. Studies on metallogenic regularity of gold deposits in China also have made achievements with a long‐term work. This review aims to conclude the achievements of research on gold metallogenic regularity in China. Based on the data of about 2000 gold deposits and other ore (mineralized) occurrences, gold deposits in China were classified into five prediction types: gold deposits genetically related to granite–greenstone formation, gold deposits related to sedimentary formation (including the Carlin type and the metamorphosed clastic rock related vein gold deposit), gold deposits genetically related to volcanic rocks (including the continental and marine types), gold deposits genetically related to intrusions (including the porphyry type and the inner intrusion and contact zone related gold deposit), gold deposits of supergenesis (including fracture zone–altered rock gold deposit, placer gold deposit, gossan type gold deposit and soil type gold deposit). Statistics on precise chronology data of gold deposits indicate that there occurred 5 main periods of gold–mineralization in geological history of China. They were Neoarchean to Paleoproterozoic, Meso–Neoproterozoic, Paleozoic, Mesozoic, and Cenozoic. Gold deposits in China mainly formed in the Mesozoic and the Cenozoic. On the studies of the spatial‐temporal distribution characteristics of gold deposits, 53 gold‐forming belts were delineated in China. The metallogenic regularity of gold deposits was preliminarily summarized and 71 gold metallogenic series were proposed in China. This suggests that it is necceary to deepen the study on metallogenic regularity of gold deposits and to provide the theory guide for the ore–prospecting for gold resources in China.

A Giant Gold System, Geita Greenstone Belt, Tanzania

[Extract] Archean greenstone belts are a well-known source of gold deposits. If we ignore the giant Witwatersrand gold system we can confidently say that the majority of Archean gold comes from greenstone belts. Even though as a general rule greenstone belts are highly prospective for gold some greenstone belts have proved to be much more productive than others. For example most of the gold in Canada's Superior Province comes from Abitibi Greenstone Belt, particularly from Timmins area (e.g. Wyman, 2003). Similarly, most of the gold mined from Australia's Yilgarn Craton comes from the Kalgoorlie camp which accounts for more than half of the gold mined so far (Philips et al., 1996) in the entire craton. Interestingly, although far apart, the geology and mineralization styles of gold deposits in both areas are very much alike suggesting that the processes leading to the formation of giant ore systems must be similar starting from the ground preparation to the mineralization process. In the Tanzania Craton the giant Bulyanhulu gold deposit is also similar to the giant deposits found in the Timmins and Kalgoorlie areas, respectively. That is, lode gold mineralization style, mafic host rocks, ages, map scale patterns, deformation styles and the short premineralization crustal history are all largely similar (e.g. Bateman and Bierlein, 2007). Bulyanhulu is much more similar to the Kalgoorlie camp in the sense that it consists of one major gold deposit, while the Timmins camp is made of a large number of smaller gold deposits. These similarities between three giant gold camps situated on three different continents may indicate that in order to form giant gold deposits certain conditions need to be satisfied. However, that is not always the case and the gold mineralization found in Geita Greenstone Belt does not follow the typical pattern of Archean lode gold deposits. Geita Greenstone belt contains a minimum of fifteen gold deposits which may resemble the Timmins camp, but the mineralization style, alteration, structures and host rocks are different. The mineralization in Geita Greenstone belt is preferentially hosted within deformation zones developed along the contact of banded ironstones and porphyries of various compositions rather than along some major shear systems. The structures associated with the mineralised system are minor, the alteration zone is restricted to the mineralised zone, quartz veins are rare or missing although silicification is common.

The Brevity of Hydrothermal Fluid Flow Revealed by Thermal Halos around Giant Gold Deposits: Implications for Carlin-Type Gold Systems

The duration of hydrothermal activity required to form ore deposits is poorly constrained. We demonstrate that thermochronology data, coupled with thermal modeling, can be used to constrain the duration of hydrothermal fluid flow. Apatite fission-track (AFT) thermochronology data define a conductive halo around an Eocene hydrothermal system that formed the Betze-Post gold deposit on the northern Carlin trend in Nevada. The premineralization Goldstrike stock acted as an essentially impermeable side to the auriferous Carlin hydrothermal system. The hydrothermal fluid conductively heated the intrusion over the time that it flowed past it. To derive first-order estimates for the maximum duration of this flow we numerically modeled one-dimensional conductive heat flow into the intrusion and used the results to forward model ensuing AFT annealing. Modeled levels of annealing were compared to AFT dates and track length data measured across the intrusion. Our results indicate that the episode of main ore-stage hydrothermal fluid flow (mean temperature of 200°C) that formed the ~1,150 metric ton (t) Betze-Post gold deposit had a maximum duration of <15 to 45 ka. The average gold flux over this period was ~80 to 30 kg yr−1, comparable to that measured in the deep reservoirs of several modern geothermal fields. Conservative estimates of gold concentration in the main ore-stage fluids imply that fluid upflow rates and total advective heat flow were also comparable to modern geothermal systems. This suggests that the most important factors for generating the large gold deposits of the northern Carlin trend were a large and/or continuous source of gold, and a very efficient means of removing it from the fluid, rather than the hydrologic system itself. The short duration of main ore-stage fluid flow is unlikely to represent a steady-state convective system. Instead, it most likely reflects a transient period of flow following slip and permeability generation along the steeply dipping Post-Genesis fault system that hosts many of the deposits along the northern Carlin trend. A sudden increase in the permeability of a fault may have led to a transitory period of peak fluid temperature as the fault initially tapped meteoric fluid that had resided at depth and had thermally equilibrated with the host rocks. With continued convection the flow drew cooler, less rock-buffered meteoric water down from higher in the system.

Geology, geochemistry and ore genesis of the Wenyu gold deposit, Xiaoqinling gold field, Qinling Orogen, southern margin of North China Craton

The Wenyu giant gold deposit is hosted in the Precambrian Taihua Supergroup metamorphic rocks within the Xiaoqinling terrane (Qinling Orogen), on the southern margin of the North China Craton. The mineralization can be divided into three stages: quartz–pyrite veins early, quartz–sulfide veins middle (main), and carbonate–quartz veinlets late, with gold being mainly introduced in main stage. Quartz formed in two earlier stages contains three compositional types of fluid inclusions, i.e. pure CO2, CO2–H2O and NaCl–H2O, but the late-stage minerals only contain the NaCl–H2O inclusions. The inclusions in quartz formed in the early, main and late stages yield total homogenization temperatures of 262–417°C, 236–407°C and 114–239°C, respectively, with salinities no higher than 13wt.% NaCl equiv. Trapping pressures estimated from CO2–H2O inclusions are 139–399MPa and 111–316MPa in the early and main stages, corresponding to mineralization depths of 14km and 11km, respectively. Fluid boiling and mixing caused rapid precipitation of sulfides and native Au. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition, and from metamorphic to meteoric, as indicated by decreasing δ18Owater values from early to late. The carbon, sulfur and lead isotope compositions suggest the hostrocks within the Taihua Supergroup to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, fluid inclusion and C–H–O–S–Pb isotope geochemistry, we conclude that the Wenyu gold deposit was an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic–Early Cretaceous continental collision between the North China and Yangtze Cratons.

Hidden gold

How the giant sediment-hosted gold deposits of Nevada were formed is disputed. A model linking regional tectonics with magma emplacement and fluid generation at depth suggests that these deposits result from an optimal coincidence of processes.

Precious Metals in Modern Hydrothermal Solutions and Implications for the Formation of Epithermal Ore Deposits

ABSTRACT We determined the concentrations of gold, silver, arsenic, antimony, and mercury in deep hydrothermal solutions (~1 km depth, 200° to &amp;gt;300°C) from active geothermal systems in the Taupo Volcanic Zone, New Zealand, and Ladolam, Lihir Island, Papua New Guinea. The wide range of concentrations in the New Zealand systems and the stable isotope signatures at Ladolam confırm that magmas are an important source of high concentrations of gold and silver in hydrothermal solutions. The Rotokawa geothermal system in New Zealand has the highest hydrothermal fluxes of gold (~30–100 kg/yr) and silver (~5000–11,000 kg/yr), which, if they remained constant, could match the metal inventories of the largest ore deposits in the world in &amp;lt;50,000 years. This relatively short time span is comparable to the amount of time required to account for the known gold resource in ores at Ladolam, which has a slightly lower gold flux (~25 kg/yr). The fact that a giant gold deposit exists at Ladolam, rather than at Rotokawa, demonstrates the importance of fluid focusing and effıcient metal deposition in the formation of epithermal gold and silver ore deposits.

Age and source constraints for the giant Muruntau gold deposit, Uzbekistan, from coupled Re-Os-He isotopes in arsenopyrite

The Muruntau gold deposit, Uzbekistan, is one of the largest gold deposits known worldwide, but its origin remains controversial. We used Re-Os arsenopyrite geochronology to precisely determine the age of main-stage gold mineralization at Muruntau to be 287.5 ± 1.7 Ma, which overlaps the emplacement of proximal post-tectonic granitoid magmatism. Additionally, we suggest that arsenopyrite growth may have occurred over an interval of at least 2 m.y. Os initial ratios derived from arsenopyrite were coupled with He isotopic data from fluid inclusions within arsenopyrite to constrain the source of ore metals and fluids. Muruntau arsenopyrite yields relatively unradiogenic initial Os (0.37 ± 0.27) and elevated 3He/4He ratios (0.23–0.33 R a) relative to purely crustal Os-He reservoirs. These data suggest the presence of a mantle-derived component in the ore system that was probably introduced during the generation of the granitoid magmas. These new timing and source constraints provide important new insight into the generation of this giant gold deposit, and they necessitate reexamination of genetic models for Muruntau and potentially other giant “orogenic gold” deposits worldwide.

Igneous Geology of the Carlin Trend, Nevada: Development of the Eocene Plutonic Complex and Significance for Carlin-Type Gold Deposits

The Carlin trend contains the largest concentration of Carlin-type gold deposits in the world. Two major controversies about these giant gold deposits have been their age, which is now firmly established as Eocene, and the source of heat, fluids, and metals, which remains debated. We present data that demonstrate an intense period of Eocene magmatism coincided in time and space with deposit formation and was arguably the primary heat source. Geologic studies over the last 40 years have emphasized the stratigraphy and structure of Paleozoic sedimentary rocks, which are the major ore hosts. However, four igneous episodes affected the Carlin trend, in the Jurassic, Cretaceous, Eocene, and Miocene. A Jurassic diorite-granodiorite laccolith and related dikes were emplaced at about 158 Ma in the northern Carlin trend. A Cretaceous granite intruded the north-central part of the trend at 112 Ma. Abundant Eocene dikes intruded along most of the trend and were accompanied by lavas in a large volcanic field along the southwest edge of the trend between ~40 and 36 Ma. Miocene rhyolite lavas erupted just west of and across the southern part of the trend at ~15 Ma. Exposed Eocene rocks consist predominantly of silicic to intermediate dikes, lavas, and epizonal intrusions, which we interpret to be sourced from a large Eocene plutonic complex underlying the Carlin trend. Eocene dikes are present in most deposits, are generally altered, but, with a few exceptions, were poor ore hosts. Distinct Eocene igneous suites, which are restricted to specific areas of the trend, are from north to south: (1) 40.3 to 39.0 Ma rhyolite to dacite dikes in the northern Carlin trend, centered approximately on the Betze-Post deposit and the richest part of the trend; (2) 37.6 Ma porphyritic rhyolite dikes including those that host ore at the Beast deposit; (3) 38.6 Ma intermediate to silicic intrusions of Welches Canyon; (4) 38.1 to 37.4 Ma andesite to dacite lavas and shallow intrusions of the Emigrant Pass volcanic field; (5) 36.2 Ma rhyolite dikes in the Emigrant Pass field that are indistinguishable from the 37.6 Ma suite except for age and location; and (6) ~37.5 Ma rhyolite to dacite intrusions and lavas of the southern Carlin trend (Rain subdistrict). Additionally, a few basaltic andesite dikes were emplaced at 37.8 Ma near Dee in the northernmost part of the trend and at 38.2 Ma near Rain. The petrography, distribution, and age of the Eocene igneous suites and aeromagnetic data indicate that each suite is underlain by a major, silicic pluton. The longer lived suites require either multiple plutons or long-lived magma chambers. All Eocene dikes cannot have come from any single magma chamber, for example, from a chamber beneath the Welches Canyon intrusions as proposed by some. In this case, some igneous suites would have been emplaced only 12 to 15 km north of the northern edge of the source pluton, would not have been emplaced above or symmetrically around the source pluton, and would be distinct in age from the proposed source pluton. These requirements are not consistent with the distribution and age of the igneous suites. The combined data for the Eocene igneous rocks require a plutonic complex about 50 km long (north-south), essentially coincident with the northern and central Carlin trend, and between 12 and 23 km across, underlying an area of ~1,000 km2. This complex was emplaced over ~4 million years that coincided with the formation of the Carlin-type deposits of the Carlin trend. Although many factors contributed to the formation of the deposits and the Carlin trend, magmatic heat was abundant in the right place and at the right time to generate the deposits. The Carlin trend may be the largest concentration of Carlin-type deposits because the Eocene igneous episode there was the largest and longest lived of the Great Basin.

Lithospheric controls on the formation of provinces hosting giant orogenic gold deposits

Ages of giant gold systems (>500 t gold) cluster within well-defined periods of lithospheric growth at continental margins, and it is the orogen-scale processes during these mainly Late Archaean, Palaeoproterozoic and Phanerozoic times that ultimately determine gold endowment of a province in an orogen. A critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle (SCLM) beneath a province at the time of gold mineralisation, as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere. A proxy for the latter is a short pre-mineralisation crustal history such that thick SCLM was not developed before gold deposition. In constrast, orogens with protracted pre-mineralisation crustal histories are more likely to be characterised by a thick SCLM that is difficult to delaminate, and hence, such provinces will normally be poorly endowed. The nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks, with back-arc basalts, transitional basalts and basanites enriched in gold relative to other rock sequences. Thus, segments of orogens with thin lithosphere may enjoy the conjunction of giant-scale fluid flux through gold-enriched sequences. Although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits, the precise siting of those giants depends on the critical conjunction of a number of province-scale factors. Such features control plumbing systems, traps and seals in tectonically and lithospherically suitable terranes within orogens.

Geodynamic processes that control the global distribution of giant gold deposits

Abstract This paper address the question of why giant gold deposits are so unevenly spread over the continents, what processes control their distribution, and how more might be found? Using the source-migration-trap paradigm, it is proposed that the regional distribution of gold deposits is controlled by fluid access to gold sources on a regional scale, and by large-scale migration mechanisms. Local distribution is controlled by migration and trap processes, not discussed in this paper. Our current levels of understanding of gold suggest a strong geodynamic control in the generation of enriched source rocks and the fluids that may carry gold, particularly the influence of subduction and accretion during orogeny. A new six-fold geodynamic classification system that emphasizes subduction and accretion processes has been used here qualitatively to assess the potential for gold-bearing source areas. The resulting classification is compared to the distribution of 181 known giant gold deposits (those with more than 100 t contained gold). The results confirm the proposition that the distribution of giant gold deposits is ultimately a function of the amount of oceanic crust consumed during the orogenic episode that built that part of the crust. Of the six geodynamic classes described, large ocean closure orogens were found to contain the most gold, with nearly half of the world’s gold held in known giant deposits. Implications for understanding ore genesis, exploration for other giant deposits, and for other empirical explanations of the distribution of gold are discussed further.

Gold Deposits in Metamorphic Belts: Overview of Current Understanding,Outstanding Problems, Future Research, and Exploration Significance

Gold Deposits in Metamorphic Belts: Overview of Current Understanding,Outstanding Problems, Future Research, and Exploration Significance

Some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration

Porphyry copper-gold, skarn copper-gold, sediment-hosted (Carlin-style) gold, breccia pipe, low-sulphidation epithermal gold, pluton-related (mesothermal or orogenic) gold vein and volcanogenic massive sulphide deposits associated with alkaline rocks are commonly broadly similar to those hosted by their calc-alkaline counterparts. In contrast, porphyry molybdenum-gold deposits are confined to alkaline igneous centres. Alkaline suites are notably deficient in high-sulphidation epithermal gold deposits and even in the advanced argillic lithocaps which host them. This is surprising, given that the required oxidised sulphur species are seemingly more abundant than in calc-alkaline igneous centres. Highly efficient buffering of acidic fluid by metasomatised alkaline rocks may offer a viable explanation. All types of intrusion-related zinc deposits also appear to be poorly developed in alkaline provinces. The characteristics of several gold and copper deposits associated with alkaline rocks, including the giant Porgera, Cripple Creek, Ladolam, Olympic Dam and Phalaborwa examples, are judged to diverge appreciably from their most closely related deposit types, rendering them arguably unique. Most of these aberrant mineralisation styles may be due to variations in magmatic-fluid compositional and liberation characteristics consequent upon the extreme diversity of ore-related alkaline magmas. Most types of gold and copper deposits developed in calc-alkaline provinces also constitute exploration targets in and around alkaline igneous centres, although porphyry copper-gold and low-sulphidation epithermal gold deposits are considered to possess the greatest potential. Perhaps of even greater interest, however, is the possibility of encountering unconventional giant gold and copper deposits which lack closely analogous examples. If already-defined aberrant deposits are truly unique, then exploration designed specifically to detect additional examples is pointless. Furthermore, exploration for new unique deposits is difficult because their defining geological parameters are unknown. Alkaline rocks within or behind calc-alkaline arcs at convergent plate boundaries probably offer the greatest exploration potential, although anorogenic intracontinental extensional settings should not be ignored.

The Giant Muruntau Gold Deposit: Geologic, Geochronologic, and Fluid Inclusion Constraints on Ore Genesis

The Giant Muruntau Gold Deposit: Geologic, Geochronologic, and Fluid Inclusion Constraints on Ore Genesis

Setting of the giant Muruntau Gold Deposit: Implications for ore genesis

Setting of the giant Muruntau Gold Deposit: Implications for ore genesis