Timing Of Gold Mineralization Research Articles

Role of metasomatized mantle lithosphere in the formation of giant lode gold deposits: Insights from sulfur isotope and geochemistry of sulfides

The Wulong deposit is one of the largest quartz vein-type gold deposits with at least 80 tons of identified gold reserves in the eastern part of the Liaodong Peninsula. Gold orebodies are mainly hosted in the Late Jurassic gneissic two-mica granite and Early Cretaceous diorite dykes, and are structurally controlled by the NNE- and NW-trending faults. Gold mineralization mainly occurs as veins with lenticular shapes and is closely associated with sulfides and Bi minerals. Previous studies on the deposit mainly focused on its geological characteristics, fluid inclusions and the timing of gold mineralization. However, the extreme enrichment mechanism of gold, the geodynamic setting and ore source of the gold deposit remain equivocal. Here we present results from geochemical studies of pyrite and pyrrhotite at Wulong to address these issues. Pyrrhotite can be grouped into euhedral (Po1) and anhedral (Po2) varieties based on the textures. Four generations of pyrite were identified based on petrographic studies: Py1 is coarse-grained subhedral to euhedral crystal coexisting with milky quartz, and Au-depleted in composition; Py2 is represented by medium-grained, subhedral to anhedral pyrite coexisting with euhedral Po1, smoky quartz and minor chalcopyrite; Py3 occurs as fined-grained anhedral grains in the quartz-polymetallic sulfide veins; Py4 occurs as veinlets or aggregates in the quartz-calcite veins and contains the lowest Au concentrations. The time-resolved LA-ICP-MS ablation depth profiles of sulfides combined with detailed petrological observations indicate that gold mainly occurs either as invisible solid solution within the crystal lattice of sulfides, to some extent, or as small blebs of native gold and electrum. The close temporal and spatial relationships among native bismuth, native gold and Bi-Te-S minerals suggest that Bi-rich melts may have significantly sequestered gold from the hydrothermal fluids in the Wulong gold deposit. Sulfides from auriferous quartz veins have a restricted Δ33S range (−0.2‰ to +0.2‰) and a mean δ34S value of +1.25‰ with a feature of the mass-dependent fractionation (MDF) of sulfur isotopes, implying that the ore-forming materials were potentially derived from the mantle lithosphere that was metasomatized and fertilized by subduction-related fluids released from slab during the Early Cretaceous. This study demonstrates the Bi-rich melts as significant gold scavengers in As-deficient ore-forming fluid, and highlights the fundamental role of the metasomatized and fertilized mantle lithosphere in the formation of giant lode gold deposits in the eastern North China Craton at ca. 120 Ma.

Apatite records metamorphic and hydrothermal fluid evolution at the large Shuangqishan orogenic gold deposit, SE China

Orogenic gold deposits are currently the world’s major source of Au, but uncertainty exists in the timing of mineralization relative to the ages of host rocks, metamorphism, and magmatism. Consequently, the origin and detailed evolution of ore-forming fluids have long been elusive. Apatite occurs widespread in various types of mineral deposits and can provide valuable information on ore genesis. Here, we present textural, high-precision in situ U-Pb geochronological, trace elements, and Sr isotope data for metamorphic and hydrothermal apatite in the Shuangqishan gold deposit in southeastern China. These data, together with U-Pb dates of metavolcanic host rocks, granitic and mafic intrusive rocks, allow us to precisely constrain the timing of mineralization and reconstruct the history of the ore-forming fluids there. The apatite crystals within metamorphic and auriferous quartz veins can be grouped into three generations according to cathodoluminescence imaging and trace element concentrations: Ap1 precipitated in the pre-mineralization metamorphic stage, whereas Ap2 and Ap3 formed in the auriferous hydrothermal stage. Metamorphic Ap1 displays a negative Eu anomaly, indicating a predominance of Eu2+ and crystallization under relatively reduced conditions. On the other hand, syn-gold hydrothermal Ap2 and Ap3 have marked positive Eu anomalies. Radiometric ages for metamorphic Ap1 are at ca. 461 Ma, whereas hydrothermal Ap2 and xenotime from auriferous quartz gave U-Pb ages of 425 ± 15 Ma and 416 ± 15 Ma, interpreted as the time of gold mineralization. Emplacement ages determined by U-Pb zircon data are 439 ± 2 Ma for granitic intrusion and 427 ± 2 Ma for a mafic dike in the mining district. Mineralization, therefore, postdates the metamorphism of local host rocks and granitic magmatism by ∼35 ± 24 m.y. and ∼14 ± 17 m.y., respectively. The synchronism of gold genesis and mafic magmatism provides additional evidence for a mantle derivation of the ore-forming fluids. The highly radiogenic 87Sr/86Sr ratios obtained for Ap1 (0.7178−0.7302) are consistent with its precipitation from a metamorphic fluid. Higher Sr concentrations (Ap2 = 1228−2884 ppm, Ap3 = 2325−3169 ppm) and positive Eu anomalies (Eu/Eu*: Ap2 = 1.03−2.84, Ap3 = 2.00−4.30) but lower and variable 87Sr/86Sr ratios in hydrothermal Ap2 (0.7100−0.7165) and Ap3 (0.7086−0.7116) are mainly ascribed to extensive fluid-wall rock exchange of Sr during mineralization. It is therefore suggested that fluid-rock reaction played a vital role in the observed positive Eu anomalies of hydrothermal apatite. Our study highlights the usefulness of apatite as a novel and robust geochronological, geochemical, and isotopic indicator of complex mineralization processes in hydrothermal gold deposits.

In-situ monazite Nd and pyrite S isotopes as fingerprints for the source of ore-forming fluids in the Jiaodong gold province

The giant Jiaodong gold province has attracted a large amount of research on its geological features, ore-forming processes and genesis. Uncertainties as to the primary sources of ore-forming fluids, and whether host rocks contribute materials to gold mineralization, are still subject to intense debate. Here, we present comprehensive in-situ sulfur isotopic studies of pyrite from the Qujia and Xincheng gold deposits, and neodymium isotopic studies of monazite from the Xiadian, Zhuangzi, Hushan, Daliuhang, and Muping gold deposits, whose timing of gold mineralization has been constrained to ca. 120 ± 5 Ma using in-situ monazite U-Pb dating. The δ34S values among Py1 (+9.0 to +9.9‰), Py2 (+8.4 to +10.7‰) and Py3 (+6.9 to +12.3‰) are similar, showing consistence with that of other deposits in the Jiaodong gold province. It indicates that these gold deposits share the same dominant sources of sulfur and/or ore-forming fluids, potentially being exsolved from the contemporaneous magmas. Slightly wide range of δ34S for Py3 is likely due to the partially closed deposition spaces and intensive fluid-rock interaction. Hydrothermal monazite is intergrown with pyrite in the orebodies, suggesting that they were precipitated simultaneously from the same fluids. Our newly published Sm-Nd isotopic studies on monazite yielded inconsistent values of εNd (t = 120 Ma) among the Zhuangzi (−25.5 to –22.6), Xiadian (–23.3 to −20.2), Hushan (−20.6 to −18.4), Muping (−20.5 to −17.3) and Daliuhang (−13.7 to −11.6) gold deposits. These in-situ monazite Nd isotopes overlap with whole-rock Nd isotopes of their corresponding host rocks, indicating the material contribution of host rocks to the gold mineralization. This study provides robust evidences showing that the ore-forming fluids of the Jiaodong gold deposits share the same primary origin, but incorporate nonnegligible abundance of materials (REE, and potentially ore-related elements, such as Au, As, Fe) from the host rocks upon ascending, due to intensive fluid-rock interaction.

SIMS U-Pb dating of vein-hosted hydrothermal rutile and carbon isotope of fluids in the Wulong lode gold deposit, NE China: Linking gold mineralization with craton destruction

Wulong is the largest lode gold deposit in the Liaodong Peninsula, northeastern North China Craton (NCC). Gold mineralization mainly occurs in the quartz-sulfide veins, which are hosted in Jurassic monzogranite and Early Cretaceous diorite dikes. Here, rutile grains are firstly identified in the auriferous quartz-pyrite vein. The vein-hosted rutiles have textural associations with quartz, chlorite, pyrite and Bi-sulfosalts and host fluid inclusions, indicating that they are unequivocally of hydrothermal origin and co-precipitate with gold. The rutile grains are characterized by high W and V concentrations, and U-shaped rare earth elements pattern with the greatest depletion in MREE. Due to excess Zr incorporation during fast rutile crystal growth process from the F-rich ore-forming fluids, Zr-in-rutile thermometers provide unrealistic crystallization temperatures (>550 °C), which are much higher than the previous homogenization temperatures data of fluid inclusions (Yu et al., 2018). All these geochemical signatures also support that rutiles formed from the hydrothermal fluids. The δ13C values of CO2 gases in low-salinity, aqueous-carbonic fluid inclusions from the mineralized quartz range from –9.6‰ to –1.7‰ (average = –5.7‰), indicating mantle/magmatic sources for the ore-forming fluids. SIMS U-Pb dating yields a more precise and robust age of 122.3 ± 1.1 Ma (n = 23, MSWD = 0.82) for the gold mineralization at Wulong. This new date is roughly coeval with the ore-hosted diorite dikes and the Sanguliu granitic pluton (most in 125–120 Ma). Such close temporal association provides additional weights of evidence for a magmatic affinity to the gold formation. Regionally, the rutile U-Pb age indicates that the gold mineralization occurs in an extensional tectonic regime, caused by the thinning and destruction of the lithosphere beneath the NCC. Meanwhile, the timing of gold mineralization is the same as the peak age of NCC destruction. Therefore, we propose that the Wulong deposit has a genetic link with this craton destruction. This is similar to numerous other Early Cretaceous gold deposits across the NCC, such as those in the Xiaoqinling and Jiaodong districts. Our study indicates that rutile is a robust U-Pb chronometer for the lode gold deposit, but may be not a good geothermometer in the case of F-rich hydrothermal fluid system.

Caledonian (Early Paleozoic) veins overprinted by Yanshanian (Late Mesozoic) gold mineralization in the Jiangnan Orogen: A case study on gold deposits in northeastern Hunan, South China

The Jiangnan Orogen, situated between the Yangtze and Cathaysia blocks in South China, is an important gold-polymetallic metallogenic belt in China. Like many gold deposits hosted in Precambrian rocks in eastern China, the timing of gold mineralization in the Jiangnan Orogen, mostly hosted by Neoproterozoic rocks, has been controversial. A number of previous geochronological studies have suggested that mineralization ages range from Neoproterozoic to Cretaceous, with Caledonian (Early Paleozoic) and Yanshanian (Jurassic – Cretaceous) being considered most important. As Caledonian is the most important period of regional metamorphism, and Yanshanian is the most important period of granitic magmatism, the timing of mineralization is closely related to the genetic nature (orogenic versus post-orogenic) of the gold mineralization. This paper addresses these problems by studying the ages and characteristics of ore-forming fluids of two major gold deposits (Wangu and Huangjindong) in the central part of the Jiangnan Orogen, in northeastern Hunan. Muscovite Ar-Ar dating suggests that the bulk of the quartz veins in the Wangu and Huangjindong deposits were formed at ca. > 399 – 397 Ma, i.e., during the Caledonian orogeny, whereas gold mineralization (and associated veining) took place at ca. 142 – 130 Ma, i.e., during the Yanshanian orogeny. Fluid inclusions in the barren “Caledonian veins” are characterized by the H2O-NaCl-CO2 system, homogenization temperatures of 266 – 276 °C and salinities of 5 – 5.4 wt% NaCl equivalent, similar to those found in many orogenic-type gold deposits, whereas the fluid inclusions in the gold-bearing “Yanshanian veins” (with abundant sulfides) overprinting the barren veins have a H2O-NaCl composition system, homogenization temperatures of 169 to 256 °C, and salinities from 8.7 to 15.2 wt% NaCl equivalent. It is proposed that both the Caledonian and Yanshanian veining events are controlled by the same fracture systems, with the former being formed in a relatively deep, orogenic deformation-metamorphic environment, and the latter in a relatively shallow, extensional environment accompanied by extensive granitic magmatism. Reactivation of the Caledonian structures during the Yanshanian orogeny, together with availability of sulfur and gold, possibly associated with granitic intrusions, played a key role in the formation of the gold deposits in northeastern Hunan and possibly elsewhere in the Jiangnan Orogen.

Alteration patterns linked to high-grade gold mineralization at the Wattle Dam deposit, Western Australia

Sharp physio-chemical gradients occur in Archean gold systems, yet they are often poorly defined. These physio-chemical gradients can provide windows into fluids that deposit high-grade gold mineralization. Recognizing different alteration styles and fluid-types in mineral systems helps define processes that led to the deposition of high-grade gold. Here we report on the architecture and chemical gradients across the komatiite-hosted Wattle Dam gold deposit in the eastern Yilgarn Craton, Western Australia, which is one of Australia’s highest grade-gold deposits. The deposit notably contains millimeter- to centimeter-thick gold-only veins with an absence of quartz. Whole rock geochemistry shows that high-grade gold veins are hosted in komatiite flow-margins facies with olivine orthocumulate komatiites in the footwall, interbedded graphitic shale close to the lode and komatiite basalt in the hangingwall. The komatiite flow-margin facies that hosts high-grade gold veins have been pervasively altered by stage 1 biotite-actinolite. Stage 2 gold veins cross-cut the biotite-actinolite altered komatiite and these veins contain thin (<100 µm) selvages of sodicgedrite, riebeckite, aegirine and ullmannite ± sulfates (barite and anhydrite) ± magnetite. Millimeter-thick gold-only veins are associated with the dissolution of zircon and magnetite, and precipitation of catapleiite in veins. These textures are consistent with the contention that fluids mobilized Zr and Fe and were highly reactive. Arsenic- and Sb-bearing alteration in the form of cobaltite, arsenopyrite, nickeline, gersdorffite, breithauptite and ullmannite occur as wide halos (up to 300 m) around the main lode. These As and Sb bearing-phases form in both the hangingwall komatiite basalt unit and footwall olivine orthocumulate komatiites. Arsenides and antinomides contain inclusions of Au and can be directly linked to mineralization. The diverse array of mineral assemblages associated with high-grade and low-grade gold mineralization indicates sharp chemical gradients at the time of gold mineralization. The mobility of Zr and Fe at the time of mineralization in the core of the deposit points towards the presence of alkaline fluids, whereas peripheral zones are associated with minerals associated with the near-neutral H2O-CO2 fluids, commonly linked with Archean gold systems. The generation of carbonate-undersaturated alkaline fluids in the high-grade core of the Wattle Dam deposit, may be explained by phase-separation or a CO2-poor alkaline fluid source. Either way these alkaline fluids played a critical role in mobilizing and concentrating very high amounts of gold into veins.

Geology and geochronology of the Shijia gold deposit, Jiaodong Peninsula, China

The Shijia gold deposit, classified as a Linglong-type (quartz vein-type) gold deposit, is located in the north of Qixia-Penglai gold belt in the Jiaodong Peninsula. The orebodies predominantly occurring as quartz-sulfide veins are hosted in the Early Cretaceous Guojialing amphibole-bearing monzogranite and strictly controlled by NNE- to NE-striking high-angle faults. Hydrothermal minerals include K-feldspar, quartz, sericite, pyrite, sphalerite, galena, chalcopyrite, calcite and fluorite. Based on the mineralogical, textural and field cross-cutting relationships, the mineralization process can be divided into three stages: (I) quartz-sericite-pyrite stage, (Ⅱ) quartz-sulfide-gold stage and (III) quartz-calcite-fluorite stage. Field investigation shows that the orebodies have undergone several times of deformation after their formation, resulting in the deformation and discontinuity of the orebodies. Early Cretaceous dykes, including granite pegmatite, lamprophyre, diabase and granite porphyry, are developed in the Shijia gold deposit. The crosscutting relationship between orebodies and various mafic-felsic dykes shows that their formation sequence is granite pegmatite, Au orebody, lamprophyre, diabase and granite porphyry. LA-ICP-MS zircon U-Pb dating shows that the emplacement ages of granite pegmatite, lamprophyre, diabase, and granite porphyry are 129.7 ± 1.6 Ma, 129.3 ± 1.4 Ma, 128.3 ± 1.3 Ma and 120.0 ± 1.1 Ma, respectively. These dating results are consistent with the crosscutting phenomenon observed in the field, indicating that the mineralization time of the Shijia gold deposit is between 129.7 Ma and 129.3 Ma. The timing of gold mineralization at Shijia coincides with the large-scale thinning of the lithosphere in the North China Craton during the Early Cretaceous, indicating that the formation of the deposit is mainly controlled by extensional tectonics. Because the gold mineralization was predated the emplacement of lamprophyre and diabase dykes, there might be not a direct genetic relationship between the gold mineralization and the mafic dykes in the Shijia gold deposit.

Geology, geochronology, and S-Pb-Os geochemistry of the Alastuo gold deposit, West Tianshan, NW China

The Alastuo gold deposit, located in the Narati region of the Chinese West Tianshan, is a newly discovered gold deposit within the world-class Tianshan gold belt. The gold mineralization is hosted by an Early Carboniferous granodiorite intrusion and controlled structurally by subsidiary faults of the transcrustal North Narati Fault. The deposit consists of auriferous alteration assemblages and minor vein ores. Field relations and petrographic data suggest four stages of mineralization with gold precipitated coevally with quartz, chlorite, epidote, pyrite, and galena during the second and third stages that are characterized by tectonic transformation from ductile shearing to brittle deformation. The temperature range of gold precipitation is estimated to be 280–330 °C using chlorite geothermometry. Ten auriferous pyrite samples yielded a well-defined Re-Os isochron age of 325 ± 3 Ma and two sericite samples yielded plateau-like 40Ar/39Ar ages of 321.7 ± 3.0 Ma and 321.2 ± 2.8 Ma. These consistent ages suggest that the gold mineralization in the Narati region was emplaced in a transitional regime from subduction to continental collision between the Tarim block and Middle Tianshan terrane (325–310 Ma), rather than during the post-collisional stage as in most part of the Tianshan gold belt. Gold-bearing pyrite has an initial Osi value of 0.7 ± 0.1 and lead isotopes ratios of 17.897 to 18.723 for 206Pb/204Pb, 15.474 to 15.643 for 207Pb/204Pb, and 37.522 to 38.299 for 208Pb/204Pb, while samples of pyrite, galena, and sphalerite have 34SV-CDT of +1.9 to +7.8‰. The isotope data suggest that the sulfur and metals are most likely derived from mixed mantle and crustal sources including metamorphic devolatilization of subducted oceanic slab and overlying sedimentary rocks. The mineralization styles, structural controls, metal and sulfur sources, and the timing of gold mineralization with respect to the orogenic event all suggest that the Alastuo gold deposit represents an orogenic type deposit. This newly recognized Carboniferous orogenic gold mineralization event calls for a re-evaluation of the gold metallogeny in the Middle Tianshan.

Genesis of the Wulong gold deposit, Liaoning Province, NE China: Constrains from noble gases, radiogenic and stable isotope studies

The Wulong lode deposit contains over 80 tonnes of gold with an average grade of 5.35 g/t. It is one of the largest deposits in Dandong City, Liaoning Province in northeast China. Previous studies on the deposit focused on its geological characteristics, geochemistry, fluid inclusions, and the timing of gold mineralization. However, controversy remains regarding the origin of the ore-forming fluids and metals, and the genesis of the gold deposit. This paper presents zircon U–Pb and pyrite Rb–Sr ages and S, Pb, He, and Ar isotopic results along with quartz H and O isotopic data for all litho-units associated with the deposit. Laser ablation inductively coupled mass spectrometry measurements yielded zircon U–Pb dates for samples of pre-mineralization rocks like granite porphyry dike, the Sanguliu granodiorite, fine-grained diorite, and syn-mineralization diorite, as well as post-mineralization dolerite, and lamprophyre; their emplacement ages are 126 ± 1 Ma, 124 ± 1 Ma, 123 ± 1 Ma, 120 ± 1 Ma, 119 ± 2 Ma, and 115 ± 2 Ma, respectively. The pyrite Rb–Sr isochron age is 119 ± 1 Ma, indicating that both magmatism and mineralization occurred during the Early Cretaceous. The δ18OH2O values of ore-forming hydrothermal fluids from the quartz–polymetallic sulfide vein stage vary from 4.8‰ to 6.5‰, and the δDV-SMOW values are between −67.7‰ and −75.9‰, indicating that the ore-forming fluids were primarily magmatic. The noble gas isotope compositions of fluid inclusions hosted in pyrite suggest that the ore-forming fluids were dominantly derived from crustal sources with minor mantle input. Sulfur isotopic values of pyrite vary between 0.2‰ and 3.5‰, suggesting that S was derived from a homogeneous magmatic source or possibly from fluids derived from the crust. The Pb isotopic compositions of sulfides (207Pb/204Pb = 15.51–15.71, 206Pb/204Pb = 17.35–18.75, 208Pb/204Pb = 38.27–40.03) indicate that the Pb of the Wulong gold deposit is a mixture of crust and mantle components. Geochronological and geochemical data, together with the regional geological history, indicate that Early Cretaceous magmatism and mineralization of the Wulong gold deposit occurred during the rollback of the subducting Paleo-Pacific Plate, which resulted in lithospheric thinning and the destruction of the North China Craton (NCC), which indicates that the deposit is of magmatic–hydrothermal origin.

Geochronological constrains on the timing of magmatism, deformation and mineralization at the Karouni orogenic gold deposit: Guyana, South America

The Karouni deposit is located in central Guyana 35 km to the W of the former producing 5 Moz Omai mine and is interpreted to be an orogenic gold deposit. It is hosted in Rhyacian aged (2.2 to 2.1 Ga) volcano-sedimentary and intrusive rocks metamorphosed to greenschist facies. Detailed structural and crosscutting relationships, coupled with robust, new U-Pb geochronology on intermediate to felsic intrusive rocks and hydrothermal minerals from the Karouni camp have constrained the structural evolution of the deposit and provided a new age for gold mineralization with important implications for the structural framework and timing of gold mineralization throughout the region. Magmatism within the 200 km2 of the Karouni camp progressed from early, synvolcanic intermediate composition dikes at ∼2147 Ma to a major voluminous pulse of felsic magmatism coeval with regional deformation during the Trans-Amazonian Orogeny between 2120 and 2088 Ma. A late pulse of granitic magmatism at ∼1950 Ma may be related to a post orogenic event. Inherited zircons within the felsic intrusive rocks indicate assimilation of crust as old as 2223 ± 32 Ma. Gold mineralization associated with camp scale D2 deformation has been dated to 2084 ± 15 Ma on the basis of U-Pb geochronology of hydrothermal titanite. These results show gold mineralization is coeval with felsic magmatism and contemporaneous with a major pulse of orogenic gold mineralization in the Birimian Province of West Africa.

Zircon U–Pb–Hf–O and molybdenite Re–Os isotopic constraints on porphyry gold mineralization in the Bilihe deposit, NE China

The Bilihe gold deposit in Inner Mongolia is situated in the Central Asian Metallogenic Domain. Its major orebody II is a porphyry-type body, spatially and temporally associated with granodiorite porphyry and granite aplite. In this study, the timing of gold mineralization is precisely constrained by using the zircon U–Pb dating for pre-mineralization intrusions and the molybdenite Re–Os dating for later molybdenite veins. Furthermore, zircon Hf–O isotope analyses have also been carried out to decipher the nature of primary magma. Zircon U–Pb dating shows that the granodiorite porphyry and the granite aplite were emplaced at 269 ± 2 Ma and 270 ± 2 Ma, respectively, indicating the gold mineralization occurring no earlier than 269 Ma. Meanwhile, molybdenite veins are developed within the fractures and commonly cut across the auriferous veins. Thus, combined with a molybdenite Re–Os isochron age of 268 ± 1 Ma, the gold mineralization in the Bilihe deposit can be precisely restricted to ca. 269 Ma. Zircon εHf (t) values are mostly positive (1.6–11.3), along with high δ18O values of 6.20–7.63‰, suggesting a mixed source between mantle materials and ancient continental crust (such as the Bainaimiao Group) for the Bilihe magma. It is also supported by the presence of the captured detrital zircons in these intrusions. Given a universally metallogenic environment for porphyry gold deposits, a thicken crustal setting related to the collisional intermission of the Paleo-Asian Ocean is favored to interpret the formation setting of the Bilihe deposit.

Zircon U-Pb ages and Hf isotope data from the Kukuluma Terrain of the Geita Greenstone Belt, Tanzania Craton: Implications for stratigraphy, crustal growth and timing of gold mineralization

The Geita Greenstone Belt is a late Archean greenstone belt located in the Tanzania Craton, trending approximately E-W and can be subdivided into three NW-SE trending terrains: the Kukuluma Terrain to the east, the Central Terrain in the middle and the Nyamullilima Terrain in the west. The Kukuluma Terrain, forms a NW-SE trending zone of complexly deformed sediments, intruded by the Kukuluma Intrusive Complex which, contains an early-syntectonic diorite-monzonite suite and a late-syntectonic granodiorite suite. Three gold deposits (Matandani, Kukuluma and Area 3W) are found along the contact between the Kukuluma Intrusive Complex and the sediments. A crystal tuff layer from the Kukuluma deposits returned an age of 2717 ± 12 Ma which can be used to constrain maximum sedimentation age in the area. Two granodiorite dykes from the same deposit and a small granodiorite intrusion found along a road cut yielded zircon ages of 2667 ± 17 Ma, 2661 ± 16 Ma and 2663 ± 11 Ma respectively. One mineralized granodiorite dyke from the Matandani deposit has an age of 2651 ± 14 Ma which can be used to constrain the maximum age of the gold mineralization in the area.The 2717 Ma crystal tuff has zircon grains with suprachondritic 176Hf/177Hf ratios (0.28108–0.28111 at 2717 Ma) and positive (+1.6 to +2.6) εHf values indicating derivation from juvenile mafic crust. Two of the granodiorite samples have suprachondritic 176Hf/177Hf ratios (avg. 0.28106 and 0.28107 at 2663 and 2651 Ma respectively) and nearly chondritic εHf values (avg. −0.5 and −0.3 respectively). The other two granodiorite samples have chondritic 176Hf/177Hf ratios (avg. 0.28104 and 0.28103 at 2667 and 2661 Ma respectively) and slightly negative εHf values (avg. −1.1 and −1.5 respectively). The new zircon age and isotope data suggest that the igneous activity in the Kukuluma Terrain involves a significant juvenile component and occurred within the 2720 to 2620 Ma period which, is the main period of crustal growth in the northern half of the Tanzania Craton.

Hydrothermal alteration and timing of gold mineralisation in the Rumbia Complex, Southeast Arm of Sulawesi, Indonesia

The Rumbia Mountains, which in this study named Rumbia schist Complex is an east-west oriented, composed by a high-pressure/low-temperature, and a medium-pressure/low-temperature metamorphic rocks. Identified as mica schist, glauchopane schist, and green schist. Rumbia complex known as the location of gold deposits prospects discovered by local communities since 2007. The results of research showed that the metamorphic rocks are as hosts. There are two phase of gold mineralization that occurs in this area, namely: 1) Associated with tectonic deformation and metamorphic rocks exhumation, and 2) gold-related hydrothermal deposits. Radiometric age dating used 40Ar/39Ar geochronology, indicate that the first of gold mineralisation in the Rumbia Complex occurred ∼23 million years ago, and the second gold mineralisation were subsequently overprinting at 7 million years ago.

World-class Xincheng gold deposit: An example from the giant Jiaodong gold province

The Jiaodong gold deposits are currently the most important gold resources (with Au reserves of >4000 t) in China, and the leading gold-producing country globally (with Au production of ∼428 t in 2013). Jiaodong is also considered as perhaps the only world-class to giant gold accumulation on the planet where relatively young gold ores (ca. 130–120 Ma) were deposited in rocks that are 2 Ga older. The Xincheng world-class high-grade gold deposit, with a proven reserve of >200 t gold, is one of the largest deposits in the giant gold province of the Jiaodong Peninsula. It is located in the northwestern part of the Jiaobei Uplift, and hosted by ca. 132–123 Ma Xincheng quartz monzonites and monzogranites. Ore zones are structurally controlled by the NE-trending and NW-dipping Jiaojia Fault and subsidiary faults, and are mainly restricted to the footwall of the fault. The dominant disseminated- and stockwork-style ores are associated with strong sericitization, silicification, sulfidation and K-feldspathization, and minor carbonate wallrock alteration halos. The four mineralization stages are pyrite–quartz–sericite (stage 1), quartz–pyrite (stage 2), quartz–polysulfide (stage 3) and quartz–carbonate (stage 4). Gold occurs dominantly as electrum, with lesser amounts of sulfide-hosted native gold and rare native silver and argentite, normally associated with pyrite, chalcopyrite, galena and sphalerite: the latter with proven resources of about 105 t Ag, 713 t Cu, and 5100 t S.There are three types of ore-related fluid inclusions: type 1 aqueous-carbonate (H2O–CO2), type 2 aqueous (liquid H2O + vapor H2O), and type 3 CO2 (liquid CO2 and vapor CO2) inclusions. Homogenization temperatures range from 221 to 304 °C for type 1 inclusions, with salinities of 2.4–13.3 wt.% NaCl eq., and bulk densities of 0.858–1.022 g/cm3. The δ34SCDT values of hydrothermal sulfides are 4.3–10.6‰ and δ18O values of hydrothermal quartz have a median value of 13.0‰. δD values of fluid inclusions in hydrothermal quartz have a median value of −75‰. Calculated δ18Owater has a median value of 5.2‰. The timing of gold mineralization at the Xincheng gold deposit is younger than 123 ± 1 Ma, and likely between 120.9 and 119.9 Ma.A minerals system genetic model for the probable epizonal orogenic Xincheng deposit suggests an initial medium temperature, CO2-rich, and low salinity H2O–CO2 deeply sourced metamorphic ore fluid associated with dehydration and decarbonization of subducting Paleo-Pacific lithosphere. The Jiaojia Fault constrained the migration of ore-forming fluids and metals at the brittle–ductile transition. Fluid immiscibility, caused by episodic pressure drops, led to significant high-grade gold deposition in the giant Xincheng gold deposit.

Reply to Discussion: The timing of gold mineralization across the eastern Yilgarn Craton using U–Pb geochronology of hydrothermal phosphate minerals

Reply to Discussion: The timing of gold mineralization across the eastern Yilgarn Craton using U–Pb geochronology of hydrothermal phosphate minerals

Discussion: The timing of gold mineralization across the eastern Yilgarn Craton using U–Pb geochronology of hydrothermal phosphate minerals

The presentation of recent geochronological work on orogenic gold deposits in the Eastern Goldfields of the Yilgarn Craton, Western Australia, claims to prove that there is a single broad event of gold mineralization and that structural work demonstrating that there are a number of discrete gold mineralization events is wrong. This new data demonstrates no such thing, as this data, no doubt the best that can currently be produced, shows a very wide and inconsistent range in ages. Geochronology is not yet able to reliably separate these events, which appear to be spread over an interval of perhaps 30 Ma, up to ∼2635 Ma.

Geochemistry of lamprophyres at the Daping gold deposit, Yunnan Province, China: Constraints on the timing of gold mineralization and evidence for mantle convection in the eastern Tibetan Plateau

Cenozoic lamprophyre dykes occur widely along the Ailao-Shan-Red-River (ASRR) shear zone related to the Indian–Eurasian collision. Two generations of lamprophyres have been found at the Daping gold deposit in the southern part of the ASRR shear zone and have been investigated by using phlogopite 40Ar/39Ar dating and whole-rock major and trace element as well as Sr and Nd isotope geochemical analyses. The 40Ar/39Ar plateau ages of phlogopite from the two generations of lamprophyres bracket the emplacement of auriferous quartz veins in the Daping deposit between 36.8±0.2Ma and 29.6±0.2Ma, consistent with the timing of gold mineralization in other parts of the ASRR shear zone. Geochemical data suggest that these lamprophyres most likely originated from a subduction-modified mantle source consisting of phlogopite-bearing spinel lherzolite, which underwent partial melting with contributions from crust materials. In particular, the second generation lamprophyres are characterized by more primitive geochemical features than the first, suggesting that secular source evolution probably resulted from post-collisional slab break-off mantle convection and remelting from ascending asthenosphere after subducted lithosphere break-off. Widespread and episodic occurrences of lamprophyres and other potassic volcanism in the eastern Tibetan Plateau were probably related to the onset of transtensional tectonics along the ASRR shear zone during Oligocene. A genetic model involving transtensional tectonics has been proposed for lamprophyres and gold mineralization in the ASRR shear zone.

Timing, tectonic implications and genesis of gold mineralization in the Xincheng gold deposit, China: C–H–O isotopes, pyrite Rb–Sr and zircon fission track thermochronometry

The Xincheng gold deposit located at the northwestern edge of the Jiaodong Peninsula in the North China Craton has a reserve of ~96t Au and is among the largest in the Jiaodong gold province. Here, disseminated- and stockwork-style ores are hosted in Mesozoic granitoids. The mineralization and alteration are largely controlled by the regional Jiaojia fault. The C–H–O isotope values in the ores indicate that the ore-forming fluids were derived mainly from magmatic sources. New Rb–Sr geochronological data on hydrothermal pyrite from the Xincheng deposit presented in this study indicate that the main gold mineralization occurred between 126Ma and 122Ma. The zircon fission track of convergent ages and decomposed divergent ages from the ores and altered rocks show four groups of ages: ~135Ma, ~124Ma, 96–75Ma, and 66–52Ma. The ~135Ma is related to the exhumation and cooling of the Linglong granitoids. The ~124Ma is considered to represent the principal stage of gold mineralization, and is consistent with the pyrite Rb–Sr ages. The younger ages of 96–75Ma and 66–52Ma resulted from subsequent annealing caused by later tectonic activity. The timing of gold mineralization in the Xincheng gold deposit broadly coincides with the switch in stress field in eastern China from extension to transpression, resulting from the change in subduction direction of the Pacific Plate from NE–SW to NW–SE, and marked by extension-related voluminous magmatism associated with the Cretaceous giant igneous event in eastern China.

Laser Ablation ICP‐MS U‐Pb Zircon Geochronology of Granitoids and Quartz Veins in the Shihu Gold Mine, Taihang Orogen, North China: Timing of Gold‐mineralization and Tectonic Implications

AbstractThe Shihu gold deposit, situated in the Taihang Mesozoic orogen of the North China Craton (NCC), is hosted by ductile‐brittle faults within Archean metamorphic core complex. The deposit is characterized by gold‐bearing quartz‐polymetallic sulfides veins. The Mapeng granitoids stock and intermediate‐basic dikes intruded the metamorphic basement rocks, and are spatially related to gold mineralization. Detailed laser ablation inductively coupled plasma mass spectrometry (LA ICP‐MS) U‐Pb zircon ages of the granitic rocks, dykes and mineralized quartz veins in the studied area reveal its magmatic and mineralized history. The mineralized quartz veins contain inherited zircons with ages of about 2.55 Ga and 1.84 Ga, probably coming from the basement. These two Precambrian events are coeval with those in other parts of the NCC. The Mapeng granitoid stock, the largest intrusion in the area, was emplaced at ca. 130 Ma, and is coeval with magmatic zircon populations from diorites and quartz diorite pophyrites in the same region. The ca. 130 Ma magmatism and gold mineralization were most likely related to an underplating event that took place in the Taihang orogen at Late Mesozoic. The timing of gold mineralization with respect to felsic magmatism in the area is similar to those observed in other major gold‐producing provinces in the NCC. This episode is simultaneous with those in the eastern margin of NCC, indicative of a widespread late Yanshanian metallogenic event that was a response to the Early Cretaceous lithosphere in the eastern NCC, in which the mesothermal gold deposits were formed from similar tectono‐magmatic environments.

40Ar/39Ar evidence for the timing of Paleoproterozoic gold mineralisation at the Sandpiper Deposit, Tanami region, northern Australia

At the Sandpiper gold deposit in the Tanami region of northern Australia sericite is intimately intergrown with arsenopyrite in gold-bearing quartz veins and breccias, suggesting sericite crystallisation synchronous with gold-bearing fluid flow. This ore-stage sericite yields a 40Ar/39Ar plateau age of 1785 ± 32 Ma (2σ including both analytical and systematic uncertainties). Recalculation using revised and more precise values for the 40K decay constants and the age of the Fish Canyon Sanidine standard shifts the age to 1794 ±12 Ma (2σ including all known uncertainties). Given the possibility of post-mineralisation isotopic resetting this age can be conservatively interpreted as a minimum constraint on the timing of gold deposition although, given local geological relationships and estimates for the argon retentivity of white mica, we consider complete isotopic resetting to be unlikely. The preferred interpretation is, therefore, that the sericite 40Ar/39Ar age indicates the timing of gold mineralisation. Thesericite age accords with a limited dataset of 207Pb/206Pb xenotime ages of ca 1800 Ma from other gold deposits in the Tanami region, interpreted as mineralisation ages. The agreement between independently derived ages from several gold deposits lends support for a widespread gold-mineralising event at ca 1800 Ma in the Tanami region.