Carlin-type Deposits Research Articles

Flotation separation of pyrite and carbonate minerals from a carlin-type gold deposit in Guizhou by a new combined collector and its adsorption mechanism

Flotation separation of pyrite and carbonate minerals from a carlin-type gold deposit in Guizhou by a new combined collector and its adsorption mechanism

Consistent crystal orientation of core and rim pyrites indicates an epitaxial growth of rim in Carlin-type gold deposits

Consistent crystal orientation of core and rim pyrites indicates an epitaxial growth of rim in Carlin-type gold deposits

Revealing Yukon’s hidden treasure: an atomic-scale investigation of Carlin-type gold mineralization in the Nadaleen Trend, Canada

AbstractThe invisible-gold deposits known as Carlin-type are becoming more important as easier to find deposits are progressively depleted. The combination of the invisible nature of the Au in these deposits, as well as the limited surface indicators of these deposits, makes exploration to find new Carlin-type deposits extremely difficult. Comprehensive mineralization models are essential to find new Carlin-type deposits in similar geologic settings. The Nadaleen Trend of Yukon, Canada, is one such district where an improved understanding of this deposit type has led to new discoveries. Previous studies compared and contrasted the tectonic setting, host rock depositional setting, structural preparation, and mineralization style of the Nadaleen Trend with those in Carlin-type localities, Nevada. However, the comparisons at an atomic scale, between Carlin-type Au deposits in the Nadaleen Trend and those in Nevada, has yet to be investigated. This study fills this knowledge gap by combining high resolution microanalytical techniques with atom probe tomography to examine the distribution of Au and other trace elements in the Nadaleen Trend, compare them to a representative Carlin-type deposit in Nevada (Turquoise Ridge), and determine how widespread the mineralization model is. Our findings show that in the Nadaleen Trend, as in Nevada, Au is generally directly linked with As at the macro to atomic scale, and is incorporated into As/Au rich overgrowths on sedimentary/diagenetic pyrite. Gold-rich pyrite rims in the Nadaleen Trend are generally smaller than those found in Nevada (0.5–2 µm vs > 10 µm), although the ore grades appear comparable. We find that the Au in the pyrite of the Nadaleen Trend is homogenously distributed (i.e. lattice bound) at the atomic scale, but that there is a notable enrichment of As surrounding individual Au atoms. These findings are in agreement with those from previous work on a representative deposit in Nevada, and support the assertation that As is the key ingredient in facilitating the incorporation of Au into the pyrite lattice. Arsenic as an essential component in the trapping mechanisms of Au in CTG deposits, is something that has been as to yet underappreciated in the current models of CTG deposit formation.

Geochemical Evidence of Ore-Forming Processes in the Shuiyindong Gold Deposit of Southwest Guizhou Province, China.

The Shuiyindong deposit is one of the ultralarge Carlin-type gold deposits in Southwest Guizhou Province, China. Gold mineralization mainly occurs in the Permian Longtan Formation and the early Triassic Yelang Formation. It is controlled by both strata and faults. Detailed studies of the mineralogy and geochemistry characteristics of the Shuiyindong deposit are conducted to investigate the ore-forming process. Arsenian pyrite and arsenopyrite are the main Au-hosting minerals. Three types of pyrite can be recognized, including euhedral and subhedral pyrite, framboidal pyrite, and bioclastic pyrite. The euhedral and subhedral pyrite is the main Au-hosting type. The Au appears as a solid solution (Au+) and natural nanoscale gold (Au0) in the sulfide minerals. The Co/Ni ratios of sulfides (0.07-3.13) reveal that the ore-forming fluids were mainly affected by hydrothermal activity, but magmatic activity cannot be excluded. Organic matter in the ores is abundant (0.11-3.04%), which might provide sulfur for pyrite and favor an increase in the porosity and permeability of the host rocks by releasing organic acids. The REE and trace element results suggest that halogens (F and Cl) were contained in the reducing magmatic hydrothermal fluids. The sulfur isotopic data (from -8.64‰ to 27.17‰) suggest that the source of sulfur is complicated and is probably a combination of a magmatic source, the reduction of marine sulfate, and bacterial sulfate reduction. The Pb isotopic data of the sulfides indicate that Pb is from a mixture of crust and mantle sources. The obvious enrichment zones exist along the boundary faults in the geochemical map of As, implying that As may originate from the deep crust and then move to the strata with basinal fluids. By combining these results, it can be inferred that the ore-forming fluids were a mixture of basinal and deep source fluids. A probable ore-forming model of the Shuiyindong gold deposit is established.

Supergene Oxidized Gold-Silver Deposits in the Americas: Guides for Geologists

Editor’s note: The aim of the Geology and Mining series is to introduce early career professionals and students to various aspects of mineral exploration, development, and mining in order to share the experiences and insight of each author on the myriad of topics involved with the mineral industry and the ways in which geoscientists contribute to each. Abstract Supergene oxidation is a process that has created some of the largest gold and silver orebodies in the Americas, including the Carlin-type (sediment-hosted) gold deposits and Round Mountain in Nevada; Yanacocha and many similar deposits in Peru; Cerro Rico, Bolivia; and Pueblo Viejo, Dominican Republic. Oxidation can make sulfide-bearing gold-silver deposits economic by converting refractory gold-silver–bearing sulfide minerals to minerals that can be leached by dilute cyanide solutions. The use of cyanide heap leaching or tank leaching enabled open-pit mining of low-grade oxidized gold deposits starting in the 1960s. This revolutionized gold mining which, combined with the end of the dollar gold standard in 1971, led to a huge increase in gold production, particularly in the Americas where the technology has been widely applied. During weathering and oxidation of sulfide minerals, particularly pyrite, associated gold and silver form supergene minerals in the oxidation zone but are only transported over short distances (centimeters to meters) due to low solubility of the metals, so they do not form enrichment zones. Gold forms Au0 grains of 1 to 25 µm size and high fineness, as well as invisible gold associated with jarosite and iron oxyhydroxides by sorption or substitution. Silver forms halides and native silver, which may be accompanied by metastable hypogene acanthite. Silver in jarosite, alunite, and Mn oxides is refractory. The economic advantages of near-surface oxidized deposits are that they can be mined by open pit with low costs, commonly not requiring stripping or blasting. Run-of-mine ore is sent directly to leach pads, although some ores may require prior crushing and grinding with agglomeration of fine material such as clays. Oxidized ore is processed by heap leaching using dilute sodium cyanide solution and gold and silver recovered by zinc cementation or on activated carbon. Some ores require grinding and are processed by tank leaching. The hypogene sulfide minerals below the oxidized zone are typically refractory and require at least ultrafine grinding for leaching to be effective, or high-cost oxidation technology for roasting, autoclaving, or bio-oxidation. The sulfide-rich portions of deposits are often not exploited for many decades after discovery, if at all. To explore for supergene oxidized deposits, the exploration geologist requires knowledge of geology, oxide mineralogy, geomorphology, hydrogeology, and the (paleo)-climate, as well as open-pit mining, hydrometallurgy, cyanide leaching, and carbon technology, topics that are introduced here with case studies.

Zhengminghuaite, Cu6Fe3As4S12, a new sulfosalt mineral from the Zimudang Carlin-type gold deposit in southwestern Guizhou, China

Abstract Zhengminghuaite, ideally Cu6Fe3As4S12, is a new Cu-Fe arsenosulfosalt found in the Zimudang Carlin-type gold deposit in southwestern Guizhou, China. It occurs as irregular, commonly fractured grains of several to a few tens of micrometers in the brecciated gold ores and is paragenetically associated with the late ore-stage mineral assemblage, including realgar, orpiment, pyrite, chalcopyrite, arsenopyrite, aktashite, christite, quartz, and calcite. Zhengminghuaite is opaque with a metallic luster and a conchoidal or uneven fracture. The Vickers microhardness (VHN10) is 219 kg/mm2 (range 192–247 kg/mm2), and the calculated density is 4.77(5) g/cm3. In reflected light, zhengminghuaite is whitish gray with weak bireflectance (whitish gray to pinkish tinted gray), very weak anisotropy, and no internal reflection. Electron microprobe analyses give the empirical formula (Cu5.92Hg0.08)Σ6.00 (Fe1.59Hg1.07Zn0.37)Σ3.03(As3.94Sb0.02)Σ3.96S11.93 on the basis of total cations = 13, with the simplified formula Cu6(Fe,Hg,Zn)3(As,Sb)4S12. Zhengminghuaite is trigonal, with space group R3. Unit-cell parameters determined from the single-crystal X-ray diffraction data are as follows: a = 13.5373(17) Å, c = 9.2354(13) Å, and V = 1465.7(4) Å3 (Z = 3). The eight strongest lines in the X-ray diffraction pattern are [d (Å) (I, %) (hkl)]: 3.0785 (67) (003), 3.0670 (100) (131), 2.6586 (89) (132), 1.8825 (97) (134), 1.8773 (82) (520), 1.6060 (89) (135), 1.6028 (81) (523), and 1.6012 (83) (261). The crystal structure of zhengminghuaite belongs to the nowackiite group and can be described as formed by (0001) layers composed of corner-sharing FeS4 and CuS4 tetrahedra that delimit two triangular cavities. Zhengminghuaite is the Fe-dominant analog at the divalent cations site of nowackiite (Cu6Zn3As4S12) and aktashite (Cu6Hg3As4S12). Paragenetic relationships indicate that zhengminghuaite and associated Hg- and Tlsulfosalts precipitated in response to the increase in sulfidation state and decrease in temperature of the late-ore stage hydrothermal fluid.

Metal remobilization at the Nibao gold deposit in Youjiang basin, SW China: Implications from mineral texture, trace element and sulfur isotope compositions of sulfides and TiO2 polymorphs

Multistage mineralization overprinting is important for the formation of giant hydrothermal gold deposits. The Youjiang basin in SW China has undergone at least three major deformation phases in the Mesozoic, but their relationship with the large-scale gold accumulation in the region remains enigmatic. Here, we study the large Nibao gold deposit (reserve > 70 t Au) in the northern part of the basin, which has both fault-controlled and stratabound orebodies. We identified a pre-ore stage and syn-ore stage including four tectono-hydrothermal (T-H) substages (i.e., T-H stage 1, 2, 3 and 4) for the local mineralization at Nibao. The pre-ore stage is dominated by coarse-grained pyrite coexisting with TiO2 polymorphs in the Middle-Late Permian basaltic rocks. The T-H substage 1 is characterized in that the sedimentary pyrites are brecciated in bedding-parallel faults. Fluorination and silicification occur in the T-H substage 2, which is re-brecciated at the T-H substage 3 forming the highest gold grade ore in high-angle thrust fault. The T-H substage 4 presents as fault reactivation within minor calcite and pyrite deposition. Mineralogy and in-situ trace element analyses reveal that mineral dissolution and reprecipitation (incl. dolomite, auriferous pyrite and TiO2 polymorphs) is ubiquitous during the multistage tectono-hydrothermal process, and the continuous alteration overprinting may have promoted gold accumulation. This replacement process of different generations of auriferous pyrite is also recorded by their inherited sulfur isotopes, giving a narrow δ34S (−3.1 to + 2.1 ‰) range. Anatase is the main accessory phase of TiO2 polymorphs, as identified with LA-ICP-MS trace element and laser Raman spectroscopic analyses. Moreover, the anatase can been divided into two types (type-I and II) based on their texture, alteration and chemistry. The type-I anatase commonly occurring in the stratabound ore is characterized by higher Zr (mean 1,730 ppm), V (mean 1,412 ppm), and Cr (mean 110 ppm) contents than type-II that coexists with zoned pyrite in the fault-controlled ore (mean 26 ppm, 187 ppm, and 38 ppm, respectively). Additionally, W (mean 636 ppm) and Mg (10,021 ppm) in type-II are much higher than type-I ones (mean 135 ppm W and 476 Mg). These features show that the sedimentary-stage Zr-V-Cr-rich type-I anatase was dissolved via fluid metasomatism, and reprecipitated as the hydrothermal-stage W-Mg-rich and Zr-poor anatase, with gold gradually enriched. Besides, the anatase phase of TiO2 polymorphs also indicates that the Nibao gold deposit was formed under low pressure–temperature condition. Overall, we propose that the Nibao is a Carlin-type gold deposit, dominated by multistage tectono-hydrothermal events.

Application of Machine Learning to Research on Trace Elemental Characteristics of Metal Sulfides in Se-Te Bearing Deposits

This study focuses on exploring the indication and importance of selenium (Se) and tellurium (Te) in distinguishing different genetic types of ore deposits. Traditional views suggest that dispersed elements are unable to form independent deposits, but are hosted within deposits of other elements as associated elements. Based on this, the study collected trace elemental data of pyrite, sphalerite, and chalcopyrite in various types of Se-Te bearing deposits. The optimal end-elements for distinguishing different genetic type deposits were recognized by principal component analysis (PCA) and the silhouette coefficient method, and discriminant diagrams were drawn. However, support vector machine (SVM) calculation of the decision boundary shows low accuracy, revealing the limitations in binary discriminant visualization for ore deposit type discrimination. Consequently, two machine learning algorithms, random forest (RF) and SVM, were used to construct ore genetic type classification models on the basis of trace elemental data for the three types of metal sulfides. The results indicate that the RF classification model for pyrite exhibits the best performance, achieving an accuracy of 94.5% and avoiding overfitting errors. In detail, according to the feature importance analysis, Se exhibits higher Shapley Additive Explanations (SHAP) values in volcanogenic massive sulfide (VMS) and epithermal deposits, especially the latter, where Se is the most crucial distinguishing element. By comparison, Te shows a significant contribution to distinguishing Carlin-type deposits. Conversely, in porphyry- and skarn-type deposits, the contributions of Se and Te were relatively lower. In conclusion, the application of machine learning methods provides a novel approach for ore genetic type classification and discrimination research, enabling more accurate identification of ore genetic types and contributing to the exploration and development of mineral resources.

Exploration Vectors and Indicators Extracted by Factor Analysis and Association Rule Algorithms at the Lintan Carlin-Type Gold Deposit, Youjiang Basin, China

The Youjiang Basin in China is the world’s second-largest concentrated area of Carlin-type Au deposits after Nevada, USA, boasting cumulative Au reserves nearing 1000 t. This study examined the recently unearthed Lintan Carlin-type Au deposit within the Youjiang Basin. Factor analysis and association rule algorithms were used to identify exploration vectors and indicators essential for navigating this promising geological territory. In the Lintan mining area, the geological strata encompass the Triassic Bianyang, Niluo, and Xuman formations comprised clastic rocks, followed by the deeper Permian Wujiaping Formation with massive carbonate rocks. The orebodies are restricted to the F14 inverse fault, cutting through the Xuman Formation, with an additional F7 fault between the Wujiaping and Xuman formations. A total of 125 rock samples from the F14 fault and a representative cross-section were analyzed for 15 elements (Au, Ag, As, Bi, Cd, Co, Cu, Hg, Mo, Ni, Pb, Sb, Tl, W, and Zn). The elements were divided into four groups based on cluster and factor analysis. Group 1 (Co, Cu, Zn, Ni, Tl, W, and Bi) was mainly enriched in the Xuman, Niluo, and Bianyang formations controlled by sedimentary diagenesis. Group 2 (Au, As, Hg, and Sb) was concentrated in the F14 and F7 faults, representing Au mineralization. Group 3 (Pb, Ag, and Mo) was mostly enriched near the F14 and F7 faults, displaying a peripheral halo of Au mineralization, and was probability controlled by ore-forming hydrothermal activities. Group 4 (Cd and Mo) exhibited extreme enrichment along the periphery of the F7 fault. This pattern indicates the presence of a substantial hydrothermal alteration zone surrounding the fault, likely influenced by ore-forming hydrothermal processes. Additionally, Pb, Ag, Cd, Mo, and W are considered essential indicators for ore formation besides Au, As, Sb, Hg, and Tl. Twelve effective association rules were derived using the association rule algorithm, which can aid in discriminating Au mineralization. The spatial distributions of the 15 elements indicated that the F14 fault is the main ore-bearing fracture zone, while the F7 fault serves as the ore-conducting structure, channeling ore-forming fluids into the F14 fault. Faults between the Wujiaping and Xuman formations, along with their associated reverse faults, present potential prospecting targets both within and outside the Lintan Au deposit in the Youjiang Basin. Exploration geochemical data can be fully utilized by combining factor analysis and association rule algorithms, offering key guidance for prospecting Carlin-type gold and similar deposits.

Structural Control of the Getang Carlin-Type Gold Deposit in Southwest China

Structural Control of the Getang Carlin-Type Gold Deposit in Southwest China

Metallogeny and Mineral Exploration – Some Personal Reminiscences

The following personalised narrative aims to document the highlights of my involvement in some of the ground breaking developments in Economic Geology and their direct application to mineral exploration and discovery over the past half century. The story begins with my introduction to geology at secondary school and university, followed by doctoral research based on fieldwork in the Andes of South America. Then, as an employee of the Chilean Geological Survey, I got my introduction to porphyry copper deposits before returning to the UK to take up a post-doctoral research fellowship. This formative period concluded with my starting out as an independent geological consultant to the global exploration and mining industry. These early years happened to coincide with the plate tectonics revolution and its radical implications for metallogeny. I realised that porphyry copper and related deposits are integral parts of volcano-plutonic arcs generated during subduction of oceanic lithosphere, and volcanogenic massive sulphide deposits in ophiolite complexes must have formed at oceanic spreading centres. At approximately the same time, application of K-Ar dating to copper deposits led to definition of metallogenic belts and corresponding epochs in the Andes, and then established the timing of their economically important supergene oxidation and enrichment. Subsequently, using more modern and precise U-Pb zircon and Re-Os molybdenite methods, collaborative attempts were made to determine porphyry copper deposit lifespans and ages of various copper belts, deposits and prospects around the world, including the Zambian Copperbelt. The focus on porphyry copper deposits led first to an appreciation of the linkage between them and subaerial volcanism and the importance of potassic alteration as a major host of hypogene copper mineralisation, and then to geological characterisation of the increasing number of gold-rich examples. Appreciation of the importance of hydrothermal breccias in porphyry copper deposits, including recognition of mineralised diatremes, resulted in a classification scheme for breccias that may be extended to related deposit types. Extensive fieldwork showed that zones of advanced argillic alteration, termed lithocaps, constitute the shallow parts of porphyry copper systems. The role of tectonic uplift in both porphyry copper formation and subsequent supergene modification was also charted. The end result of this body of work was a porphyry copper model that can be used as a basic exploration guide. In response to a marked increase in the world gold price in the late 1970s, more effort was devoted to gold concentrations in magmatic arc terranes, commencing with epithermal gold deposits in the shallow lithocaps of porphyry copper systems. This led to an input to classification schemes for epithermal precious metal deposits and, eventually, to assignment of the three main epithermal types to specific tectono-magmatic settings. After years of speculation, porphyry gold deposits were recognised for the first time in northern Chile, followed by definition of a new gold deposit class in association with relatively reduced granitic intrusions. A magmatic-hydrothermal origin for Carlin-type gold deposits was steadfastly supported over many years, notwithstanding its unpopularity until relatively recently, culminating in a proposal for modern analogues. For decades, metallogenic provinces and corresponding epochs have been widely appreciated, but debate concerning their origin(s) persists. The nature of accompanying magmatism could well provide an adequate explanation for at least some provinces (e.g., tin, molybdenum and possibly silver), but precursor metal enrichment in the lowermost crust and/or subcontinental lithospheric mantle may well be required in the case of gold and copper provinces. The story concludes with brief commentary on mineral exploration, which has been my lifelong (pre)occupation. Requirements for success in mineral exploration are discussed, based primarily on familiarity with the circum-Pacific region, followed by analysis of the types of companies and individuals involved and the burgeoning challenges to the exploration process, which, if not remedied, will have dire consequences for future metal production and global plans for the energy transition. My involvement as a lone practitioner in both mineral exploration and metallogenic research probably says something about my independent character traits, but nonetheless has been largely unstructured and certainly unplanned. I have no hesitation in recommending a similar career path for any recent graduate who relishes adventure and is prepared to endure significant work-life imbalance.

In situ illite Rb-Sr dating indicates the coevality of Carlin-type gold deposits inside and around the isolated carbonate platform in western Guangxi, China

The western Guangxi is a crucial component of the Guizhou–Yunnan–Guangxi “Golden Triangle”(hereafter referred to as the Golden Triangle) of South China. The most discovered Carlin-type gold deposits in this region are primarily situated at the periphery of isolated carbonate platforms. The ore bodies are vein-like in form controlled by faults, and the wall rock are Triassic carbonate-bearing terrigenous clastic rocks. Recently, some gold deposits have been discovered in the interior of isolated carbonate platforms. The ore bodies are primarily stratiform hosted in sedimentary unconformities. The mineralized strata span from the Cambrian to the Permian, and the host rock include sandy and muddy dolostones, as well as a combination of sandstone, mudstone, tuff, and chert. The geological and geochemical characteristics suggest that these stratiform deposits in the interior of isolated carbonate platforms share common characteristic with Carlin-type gold deposits in China and USA. However, it remains uncertain whether these deposits are products of the one mineralization system and are coeval with those vein deposits at the periphery of the isolated platforms. To address this question, we conducted geological and isotopic dating studies on the Longhuo gold deposit and the De'e gold occurrence in the interior of isolated platforms. The Longhuo stratiform gold deposit occurs along a parallel unconformity in the Carboniferous/Devonian composed of sandstone, shale, tuff, and chert. Hydrothermal illite, quartz and auriferous pyrite fill along joints and fissures, implying that illite formed during the main ore-forming stage and its age could represent the age of gold mineralization. The stratiform orebodies of De'e gold occurrence are hosted in Cambrian sandy and muddy dolostones. Gold occurs as invisible Au in zoned pyrite and arsenopyrite, with a dominant alteration assemblage of silicification, carbonate alteration, and illitization. Hydrothermal quartz, illite and dolomite often aggregate with zoned auriferous pyrite and arsenopyrite in the most intensely altered zones, suggesting that illite formed during the main ore-forming stage and its age could also represent the age of gold mineralization. Illite LA-ICP-MS Rb-Sr dating was performed on both deposits, yielding ages of 184.16 ± 3.14 Ma for the Longhuo gold deposit and 191.21 ± 6.76 Ma for the De’e gold occurrence.Previous studies have indicated that Carlin-type gold deposits in the Golden Triangle exhibits two distinct age clusters, one ranging from 184 to 235 Ma and the other from 134 to 148.4 Ma. These dual age clusters suggest the potential occurrence of two mineralization events. The obtained ∼ 190 Ma mineralization ages for the Longhuo and De'e gold deposits in this study indicate that the Carlin-type gold mineralization within the isolated platform took place during the Early Jurassic. This aligns with the early mineralization event of gold deposits along the platform's edge, implying that gold deposits inside and around the isolated carbonate platform are products of the same mineralization system, influenced by post-Indosinian extensional events. The interior of the isolated carbonate platform holds substantial exploration potential, making it a novel direction for prospecting Carlin-type gold deposits in western Guangxi.

Metallogenic Mechanism of Carlin-Type Gold Deposit in Zhen’an-Xunyang Basin, in the South Qinling of China: Constraints of In Situ Trace Elements and S Isotopes from Newly Discovered Wangzhuang Gold Deposit

The Zhen’an-Xunyang Basin is a late Paleozoic rifted basin with a series of Au-Hg-Sb deposits that have been found, mostly along the Nanyangshan fault. Recently discovered large- and medium-sized gold deposits such as the Xiaohe and Wangzhuang deposits exhibit typical characteristics of Carlin-type gold deposits. Therefore, it is imperative to select a typical deposit for an in-depth study of its metallogenic mechanism to support future prospecting efforts targeting the Carlin-type gold deposits within the area. Based on detailed field investigation and microphotographic observation, four ore-forming stages are identified: I, low-sulfide quartz stage, characterized by euhedral, subhedral pyrite, and fine veins of quartz injected parallel to the strata; II, arsenopyrite–arsenian pyrite–quartz stage, the main mineralization stage characterized by strongly silicified zones of reticulated quartz, disseminated arsenopyrite, fine-grained pyrite; III, low-sulfide quartz stage, characterized by large quartz veins cutting through the ore body or fine veins of quartz; Ⅳ, carbonate–quartz stage, characterized by the appearance of a large number of calcite veins. In situ analysis of trace elements and S isotopes of typical metal sulfides was carried out. The results show significant variations in the trace element compositions of metal sulfides in different stages, among which the main mineralization stage differs notably from those of the Au- and As-low surrounding strata. In situ S isotope analysis reveals δ34S values ranging from 15.78‰ to 28.71‰ for stage I metal sulfides, 5.52‰ to 11.22‰ for stage II, and 0.3‰ to 5.25‰ for stage III, respectively, revealing a gradual decrease in S isotopic values from the pre-mineralization stage to post-mineralization stage, similar to those observed in the Xiaohe gold deposit. These features indicate a distinct injection of relatively low 34S hydrothermal fluids during the mineralization process. The element anomalies of the 1:50,000 stream sediment in the region revealed ore-forming element zonation changing in W→Au (W)→Hg, Sb (Au) anomalies from west to east, manifested by the discovery of tungsten, gold, and mercury–antimony deposits in the area. Moreover, conspicuous Cr-Ni-Ti-Co-Mo anomalies were observed on the western side of the Wangzhuang and Xiaohe gold deposits, indicating a potential concealed pluton related to these deposits. These lines of evidence point to a magmatic–hydrothermal origin for the Carlin-type gold deposits in this area. Furthermore, hydrothermal tungsten deposits, Carlin-type gold deposits, and low-temperature hydrothermal mercury–antimony deposits in this region are probably controlled by the same magma–hydrothermal system.

Does SW China have Carlin-type gold deposits? A micro- to atomic-scale perspective

Does SW China have Carlin-type gold deposits? A micro- to atomic-scale perspective

Age of Carlin-type gold mineralization in the Youjiang basin, South China: Constraint from hydrothermal zircon geochronology in the Badu dolerite-hosted gold deposit

Selecting a robust chronometer is crucial to determine the primary mineralization age of the deposits that have witnessed multiple hydrothermal events. The Youjiang basin of South China hosts the world’s second-largest Carlin-type gold province. However, the age of the Carlin-type gold mineralization remains highly debated, partly due to the presence of multiple hydrothermal events that may have disturbed the primary isotopic system with low durability. Hydrothermal zircon is a robust chronometer that can survive multiple hydrothermal events. To this end, in this study, we report in-situ secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb dating results of hydrothermal zircon identified in carbonate–sericite–sulfide–altered dolerite from the Badu Carlin-type gold deposit to constrain the timing of gold mineralization.The hydrothermal zircons exhibit subhedral to anhedral morphologies, sector cathodoluminescence zonings, and contain gold-related mineral assemblages of arsenian pyrite, quartz, sericite, and carbonate. Primary two-phase fluid inclusions also commonly occur in the hydrothermal zircons. Compositionally, these zircons feature relatively flat light rare-earth element (REE) patterns, high La contents, low (Sm/La)N values, and small Eu and Ce anomalies, which are different from the magmatic counterparts of the Badu pluton but consistent with those of hydrothermal zircons reported worldwide. These features indicate that the hydrothermal zircons are probably paragenetically associated with the gold mineralization. Consequently, the U–Pb ages of ca. 140 Ma of these zircons, which are much younger than those of the magmatic zircon in the fresh dolerite, can represent the timing of primary gold mineralization of Badu. Our new data suggests that there truly was an episode of gold mineralization during the Early Cretaceous in the Youjiang basin, which may have been driven by large-scale lithospheric extension in the interior of South China. This study demonstrates that hydrothermal zircon could be a robust clock for investigating the timing of magmatic rock-hosted Carlin-type gold deposits.

Multi-Phase Hydrothermal Fluid Events in the Giant Lannigou Gold Deposit, SW China: Insights from Calcite Sm–Nd Age, Trace Elements, and C-O-Sr Isotopes

The Nanpanjiang basin hosts the world’s second-largest concentration of Carlin-type gold deposits. To decipher the origin and evolution of hydrothermal fluid, this study conducted Sm–Nd dating, in-situ trace element, and C-O-Sr isotopic analyses on three types of calcite samples from the giant Lannigou gold deposit in the Nanpanjiang basin, SW China. The type-I calcite, intergrown with Au-bearing arsenian pyrite, has an Sm–Nd isochron age of 213 ± 7 Ma (MSWD = 0.81), indicating that gold mineralization occurred in Late Triassic. The type-II calcite, which coexists with high-maturity bitumens and cut through the main-stage gold orebodies, yields an Sm–Nd age of 188 ± 14 Ma (MSWD = 0.34), representing a post-ore hydrocarbon accumulation event. The type-I and type-II calcite samples have low REE contents (5.28–51.6 ppm) and exhibit MREE-enriched and LREE-/HREE-depleted patterns. Combined with their identical C-O-Sr isotopes, we suggest that hydrothermal fluids responsible for the precipitation of type-I and type-II calcite samples were derived from a mixed metamorphic fluid and meteoric water source. In contrast, the type-III calcite samples, associated with realgar and orpiment, have distinct Mn, Sr, and As contents, REE patterns, and C-O-Sr isotopic composition from the type-I and II calcites, suggestive of different fluid sources. Based on our and previously published data, we propose that the fluid evolution, gold mineralization, and hydrocarbon accumulation in the Nanpanjiang basin are closely related to the Indosinian and Yanshanian orogenies in South China.

Lithium and oxygen isotopic constraints on the source and evolution of ore-forming fluids: a case study from the Shuiyindong Carlin-type gold deposit, SW China

Lithium and oxygen isotopic constraints on the source and evolution of ore-forming fluids: a case study from the Shuiyindong Carlin-type gold deposit, SW China

Hydrothermal apatite as a robust U–Th–Pb chronometer for the Carlin-type gold deposits in the Youjiang basin, SW China

Hydrothermal apatite as a robust U–Th–Pb chronometer for the Carlin-type gold deposits in the Youjiang basin, SW China

NanoSIMS U–Pb dating of hydrothermally altered monazite: constraints on the timing of the Laozhaiwan Carlin-type gold deposit

NanoSIMS U–Pb dating of hydrothermally altered monazite: constraints on the timing of the Laozhaiwan Carlin-type gold deposit

Fractal dimension used as a proxy to understand the spatial distribution for carlin-type gold deposits

The spatial distribution of ore-forming element grades typically exhibits strong nonlinear characteristics as a result of continuous geological processes. The trend of change in ore grade sequences is a crucial indicator of the degree of enrichment of an ore deposit. Therefore, quantitative evaluation of the spatial distribution of ore-forming elements holds great significance for understanding ore-forming processes as well as for ore exploration. In this work, based on the principles of fractal theory, a MATLAB-based program to calculate fractal dimensions was developed, and fractal analysis was conducted on the gold concentration values (g/t) of 25 drill holes in the Lannigou Gold Mining Area, Guizhou, China. Rescaled range analysis and the fractal correlation integral were utilized to obtain the spatial distribution of gold concentrations in the drill holes. Rescaled range analysis revealed that the Hurst exponent (HR/S) values vary in the range of 0.58–0.97, which reflected the persistent behavior of vertical variation in gold tonnage at the studied wells. Furthermore, the relationship between gold grade distribution and associated fluctuations in the fractal dimension derived from the correlation dimension (DC) was discussed. The DC value was found to vary between 1.01 and 1.59, indicating that high-grade gold deposits were distributed along steep fractal gradients and that fractal dimension values could be used as a reliable proxy to efficiently understand the migration pathways of auriferous fluid. Studies have shown that the Hurst exponent of the Au grade sequence exhibited a strong dependence on the grade of mineralization, with gold mineralized veins persisting throughout the studied drill holes. Thus, fractal dimension gradients can serve as an important proxy for identifying the locations of potential economic gold deposits in unexplored areas. Moreover, this approach can be employed to map the distribution patterns of other types of ore deposits.