Types Of Gold Deposits Research Articles

Experimental Study on Efficient Recovery of High-Grade Sulfide Ore

A gold mine is a typical broken zone altered rock type gold deposit, with some high grade primary sulfide ore at 20~30m from the surface, and the ore grade is about 5g/t. To understand the nature of the ore, Performed the process mineralogy testing and analysis, The occurrence state of the gold mineral is very good, Most gold is bare gold, It is conducive to the enrichment and recovery; To determine the best selection process and parameters, Conducted experimental studies including Nelson reselection and flotation, Finally determined to adopt the Nielsen reselection-heavy tail flotation process, Au grade 42.15g/t, Au recovery rate of 48.92%; Reconcentration tailings after one rough selection, two sweeps, two selection, Au grade 38.26g/t, The grade of Au of tailings is 0.16g/t; The combined Au recovery rate of reselection + flotation was 97.39%, The concentrate quality and recovery indexes are all good, The benefits are considerable.

Hydrothermal origin of the Jiaojia altered rock type gold deposit: Constrains from mineralogy, geochronology and geochemistry of apatite

胶东是我国最大的金矿集中区,累计探明金资源量5000余吨,焦家式蚀变岩型金矿床提供了80%以上的金资源量,钾长石化和黄铁绢英岩化蚀变是该类矿床的重要找矿标志,但对其成因与形成时限缺乏有效约束。为探究两类蚀变的成因并限定其形成年龄,本文对典型蚀变岩型金矿床中钾长石化花岗岩与黄铁绢英岩化碎裂岩进行锆石和磷灰石LA-ICP-MS U-Pb地质年代学、磷灰石微区原位微量元素地球化学测试。结果表明,钾长石化玲珑花岗岩的锆石U-Pb年龄为155.0±1.1Ma~155.8±1.3Ma,代表了其岩浆侵位年龄;钾长石化玲珑花岗岩蚀变弱的A1型磷灰石没能得到有效年龄,而蚀变较强的A2型磷灰石U-Pb年龄为146±7Ma~147±6Ma,代表了钾长石化蚀变作用发生的时间;黄铁绢英岩化碎裂岩蚀变较弱的B1型磷灰石数量较少未形成协和年龄,强蚀变B2型磷灰石U-Pb年龄为125±6Ma,代表了黄铁绢英岩化蚀变作用发生的时间。A1型磷灰石的稀土配分曲线与未蚀变玲珑花岗岩较为一致,A2型磷灰石显示更高的轻稀土含量和更明显的Eu负异常,随着钾长石化蚀变程度增强,La/Yb比值逐渐增大,Sr含量和Sr/Y比值同步降低,暗示蚀变流体相对富轻稀土,蚀变过程磷灰石的Sr被活化迁移;B1型磷灰石的稀土配分曲线与未蚀变玲珑花岗岩相似,B2型磷灰石和未蚀变郭家岭花岗岩较为一致,轻重稀土分异明显,且Eu异常不明显,在黄铁绢英岩化蚀变过程中Sr含量、Sr/Y比值和La/Yb比值显著增高。本文认为与焦家式蚀变岩型金矿成矿相关的蚀变作用与区域岩浆作用有关,晚侏罗世玲珑花岗岩的自交代作用形成了钾长石化蚀变,早白垩世郭家岭花岗岩分异的热液沿区域性断裂迁移,导致断裂带内发生黄铁绢英岩化。

Internal Structures of Placer Gold as an Indicator of Endogenous and Exogenous Processes

The study of the internal structures of placer gold on the territory of the east of the Siberian platform, overlain by a thick cover of Mz-Kz deposits, where traditional methods of searching for gold deposits are not effective, allowed us to determine, for the first time, the stages of ore formation and conditions of its occurrence. The identified indicators of the internal structures of placer gold (structures of primary recrystallization, secondary recrystallization, thick high-grade shells) indicate that placer gold content is formed mainly due to the supply and repeated redeposition of native gold from ancient gold-bearing deposits of the Precambrian stage of ore formation to younger ones. The discovered coarse-, medium-grained, mono-grained, unclear-zonal, granulation and disintegration structures suggest a supply of gold from nearby ore sources of the Mesozoic stage of ore formation. In the weathering crust, a high-grade shell is formed. In the hydrodynamic environment, the internal structures of gold practically do not change and fully correspond to the internal structures of endogenous gold. In aeolian conditions, the internal structures are transformed. In ancient gold-bearing conglomerates, under the impact of lithostatic pressure, as well as in metamorphogenic conditions, when the PT conditions change, the internal structure changes. Thus, for the first time, on a huge factual material, it is proved that the internal structures contain extensive information both about the endogenous origin of gold (the stages of ore formation—Precambrian and Mesozoic) and about its transformation in various exogenous conditions. The identified indicator of the internal structures of placer gold for certain types of sources contribute to a more correct selection of methods for searching for ore and placer gold deposits in closed territories and assessing their prospects. The use of this method makes it possible to develop criteria for forecasting different sources and types of gold deposits based on internal structures.

Geochronology (U-Pb and Re-Os) and H[sbnd]O[sbnd]S isotopes reveal ore fluid origin and crucial role of meteoric water for Laozuoshan quartz-vein-hosted gold metallogeny in Jiamusi, NE China

The Laozuoshan auriferous sulfide-quartz veins, which are hosted in the granodiorite, monzogranite, and quartz diorite, are the only Early Cretaceous gold deposit discovered in the central Jiamusi Massif, but its origin and ore-forming processes remain unclear. Here, we integrate mineralogy, HOS isotopes, and U-Pb and Re-Os geochronology to unravel the formation of the Laozuoshan quartz-vein gold mineralization. Zircon and molybdenite from the monzogranite wallrock and gold ores yield weighted mean U-Pb and isochron Re-Os dates of 259.9 ± 2.1 Ma and 103.3 ± 2.3 Ma, respectively. Our radiometric dating suggests that the Laozuoshan quartz-vein gold mineralization was coeval with the quartz diorite (105–103 Ma) but after the monzogranite emplacement. Quartz grains from the auriferous veins of different stages yielded scattered δ18O values (5.4 to 13.0 ‰), with the δD values (fluid inclusions) ranging from –99.9 to –74.9 ‰. The δ18O values of quartz (10.9–13.3 ‰) and feldspar (9.4–11.0 ‰) from the unaltered wallrocks are similar to those (δ18Oquartz = 11.2–13.2 ‰ and δ18Ofeldspar = 10.0–10.4 ‰) from the potassic alteration halos. Meanwhile, the sericite-altered rocks have δ18O values of 12.4–12.9 ‰ (quartz) and 3.4–5.2 ‰ (sericite). Sulfides from the gold ores yielded decreasing δ34S values from 5.3 to 6.9 ‰ (early stage), through 1.0–3.5 ‰ (intermediate stage), to –4.9 to –4.4 % (late stage). The isotope data reflect a largely magmatic source for the early ore fluids, whilst the sulfur was possibly derived from the Mashan Group migmatite. The results, in combination with geologic evidence, indicate that the Laozuoshan quartz-vein gold mineralization was spatially, temporally, and genetically related to the Early Cretaceous quartz diorite, and thus can be classified as intrusion-related, magmatic-hydrothermal-vein type. In the ore-forming processes, the ascending Early Cretaceous magma may have acquired most of their sulfur and gold through assimilation of the Mashan Group migmatite. The early ore fluids derived from the quartz diorite magma may have initially focused into narrow cracks/fractures in the quartz diorite margin and then flow along the fracture system. Subsequently, meteoric water incursion led to temperature drop, boiling, oxygen fugacity increase, and chemical exchange of the resultant fluids, which facilitated gold scavenging by bismuth-rich melts and rapid precipitation as arsenopyrite-hosted electrum and gold-bismuth mineral eutectic assemblage. This study highlights the crucial role of meteoric water in formation of the magmatic-hydrothermal-vein type gold deposit.

About this title - Recent Advances in Understanding Gold Deposits: from Orogeny to Alluvium

Gold occurs in many settings, but the dynamic nature of Earth's crust means overlapping and overprinting deposit styles are common. Characterization of mineralization from an early stage becomes important, particularly where the mineralization is complex, in order to maximize exploration and project development success and mining productivity. Various techniques are used at different stages of a project to characterize gold deposits. This Special Publication offers a cross-section of some specific techniques used to investigate a variety of gold deposit types. The papers highlight both the breadth of the available techniques and their utility in deposit characterization, but also the many significant remaining questions and problems related to the exploration and research of gold deposits. Several papers include suggestions of avenues for fruitful further research, including a paper discussing a new approach to classifying orogenic gold deposits, and a paper describing archaeological applications of natural gold analyses.

The Formation of the Jiaodong Gold Province

AbstractGold deposits in Jiaodong, termed Jiaodong‐type, are tectonically located in the southeastern margin of the North China Craton. Their major features are reviewed in this paper to highlight the differences between Jiaodong deposits and other genetic types of gold deposits. The mineralization was synchronized with asthenosphere upwelling indicated by syn‐ore OIB‐like mafic dike and large‐scale crustal thinning suggested by decrease of Sr/Y from pre‐ore to syn‐ore granites. Asthenosphere upwelling induced by the roll‐back of Paleo‐Pacific Plate drove partial melting of lithospheric mantle and devolatilization, which induced the release of the ore‐forming fluids. In concomitant with magmatic records, mineralization migrated from the western Jiaobei terrane (133–127 Ma) to the eastern Sulu orogenic belt (114–108 Ma), corresponding to the eastward roll‐back of Paleo‐Pacific Plate. Gold mineralization in Jiaodong formed in the transitions of ductile to brittle deformation, rapid to slow crustal uplift, and regional compression to extension. In the regional‐scale, the gold deposits in the Jiaobei terrane are mostly situated at intersections between NE‐trending faults and EW‐trending basement faults, and gold orebodies dominantly controlled by the lithologic contacts between Precambrian metamorphic rocks and Mesozoic granites. The mineralization was dominated by the disseminated‐veinlet ores related to quartz–sericite alteration in strong cataclasite‐breccia zone, with subsidiary thick quartz‐sulfide veins developed in secondary fault zones. The ore‐forming fluids belong to a H2O–CO2–NaCl±CH4system and show minor variations in salinity among different types of ore. Structure‐fluid feedback involving fluid‐rock reaction and hydrofracturing triggered the fluid phase separation and resultant gold deposition. The Jiaodong gold deposits are distinct from orogenic and intrusion‐related gold deposits in terms of tectonic setting, origin of ore‐forming fluids, and mechanism of gold deposition.

Chronology of Alkaline Magmatism and Gold Mineralization in the Central Aldan Ore District (Southern Yakutia)

Abstract —The Central Aldan ore district (CAOD) is unique by the abundance of gold deposits associated with Mesozoic alkaline magmatism. Four types of gold deposits are established here: porphyry gold, gold–sulfide, gold–argillizite-K-feldspar–quartz, and gold–uranium. The available geochronological data on the age of igneous rocks and gold mineralization in the CAOD show that the latter formed in the period 151–120 Ma. These data also agree with the results of the U–Pb dating of the El’kon gold–uranium ore-magmatic system (143–125 Ma). Analysis of our and earlier published geochronological data showed two stages of magmatism evolution in this region. At the early stage (151–130 Ma), most of the alkali syenites, monzonites, and their analogues (sills, stocks, ring intrusions, and volcanic sequences) and ores formed. They are widespread in various deposits and massifs. In the Ryabinovyi massif, this stage is marked by the formation of most of the alkaline rocks (Aldan Complex) and ores: aegirine syenites, 151.4 ± 1.9 Ma; pyroxene–K-feldspar pegmatites, 144.8 ± 1.5 Ma; and Au–Cu ores, 137.5 ± 1.7—131.1 ± 16 Ma. The crystallization of amphibole in the syenite of the Lunnoe deposit (143.1 ± 2.0 Ma) and in the clinopyroxenite of the Inagli massif (142.4 ± 2.0 Ma) and the formation of most of the alkaline rocks of its ring framing also took place at this stage. At the Samolazovskoe deposit, this stage is marked by the formation of zircon in pseudoleucite syenite, 135.9 ± 1.9 Ma, and in different syenite porphyry phases, 141.39 ± 0.90—142.4 ± 5.0 and 134.25 ± 0.70—129.9 ± 2.6 Ma, as well as gold–skarn mineralization, 129.9 ± 2.6—134.9 ± 2.8 Ma. The same period included the formation of primary ores at the Kuranakh deposit, 136.2 ± 1.7 Ma, and the deposition of brannerite mineralization at the Lunnoe deposit, 132.4 ± 1.6 Ma. Early intrusive phases, such as potassic picrites, shonkinites, and lamprophyres, are scarce among the products of this stage of magmatism, which is possibly due to their burial beneath large volumes of later formed alkali syenites and monzonite–syenites. The second stage (128–120 Ma) was distinguished within the Ryabinovyi massif as small intrusions and dikes of olivine lamproites, shonkinite porphyry, minettes, and syenite porphyry. We revealed explosive breccias with an age of 127 Ma at the Samolazovskoe deposit. Magmatism of this stage was of limited occurrence in the CAOD and did not produce alkali syenites, monzonite–syenites, and ores. At the same time, rocks with an age of 121.1 ± 1.3—115.5 ± 1.6 Ma are widespread in the large (120 km2) Dzheltula ring massif of the Tyrkanda ore district, located east of the Central Aldan region.

GEOLOGY AND ORE CHARACTERISTICS OF LOW SULFIDATION EPITHERMAL GOLD MINERALIZATION AT TAMBANG SAWAH, LEBONG, BENGKULU PROVINCE

Abstract –– Tambang Sawah Area, Lebong Regency, Bengkulu Province, is geologically located in the Barisan mountains and Sumatra fault zone. The prospect of Tambang Sawah area lies in the physiography of the central Sumatran mountains ranges composed by the igneous rocks of the Sunda – Banda magmatic arc. This study is aimed to understand the deposit geology and ore characteristics of the gold deposit at the study area. Quartz vein mineralization of Tambang Sawah occurred in granite rock intruded into andesitic breccia rocks, with the geological structure of mineralization control in the form of joint, breccia, dike, and fault, namely the Ketahun fault that forms extentional fracture zones which were filled by hydrothermal fluid in form of quartz veins. Hydrothermal alterations that appear at the study site are typical types of alterations found in epithermal gold deposits, namely, argillic, silicified and propylitic. Sulfide minerals markers of low sulfidation epithermal type gold deposits found, namely, pyrite, calcopyrite, covelite, sphalerite and galena with colloform vein texture, cockade-crustiform, moss, and brecciated texture. Gold is interpreted to be derived from the deposition of sulfide minerals and the deposition of quartz veins, the level of gold in rocks and veins varies greatly with an average 4,8 ppm. Based on the results of ore geochemical analysis of positively correlated gold with elements Ag, Cu, Pb and Zn.
 Keywords: Mineralization, low sulfidation epithermal gold, Tambang Sawah, Lebong, Bengkulu.

A TRIASSIC OROGENIC GOLD MINERALIZATION EVENT IN THE PALEOPROTEROZOIC METAMORPHIC ROCKS: EVIDENCE FROM TWO TYPES OF RUTILE IN THE BAIYUN GOLD DEPOSIT, LIAODONG PENINSULA, NORTH CHINA CRATON

Abstract Rutile grains often occur in different types of gold deposits, and their U-Pb ages have been widely used to determine the formation time of gold mineralization. However, the origin of rutile grains in the gold deposits remains controversial. In this paper, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of U-Pb ages and trace elements on rutile grains were applied to investigate the metamorphic and hydrothermal processes of the Baiyun gold deposit (70 t Au, avg grade: 3 g/t) in the Liaodong Peninsula in the northeastern part of the North China craton. Rutile grains in the hydrothermal altered gold schist from the Baiyun deposit yielded two group ages of 1924 ± 18 and 237.0 ± 1.8 Ma, respectively. Combined with our systematic U-Pb zircon geochronological results of the ore-hosting schists and post-ore dikes, we suggest these rutile ages record a Paleoproterozoic metamorphic event and a Triassic hydrothermal gold mineralization event, respectively. The metamorphic and hydrothermal rutile grains have no obvious textural differences, but they show distinct trace element contents of Zr, W, Nb, and Ta. Combined with previous published data, we propose that high W (>1,000 ppm) and low Zr (<200 ppm) contents in rutile can be used to distinguish hydrothermal rutile from metamorphic and magmatic rutile. The newly identified ca. 237 Ma hydrothermal event is much older than the ca. 227 to 210 Ma Triassic magmatic rocks in the region, which precludes a temporal and genetic link between the Baiyun gold mineralization and the regional Mesozoic magmatism. Rather, the ca. 237 Ma gold mineralization may be associated with the Triassic orogenic metamorphism, and Baiyun is an orogenic gold deposit. The Triassic gold deposits in the northern margin of the North China craton formed by orogenesis between the Siberian craton and the North China craton. After a hiatus, the large-scale gold deposits formed during the Early Cretaceous in the North China craton due to a westward subduction of the paleo-Pacific plate beneath the craton since the Early Jurassic. Our study highlights that rutile in gold deposits may be inherited from the host rocks and/or formed by hydrothermal fluids. Distinguishing between these two different rutile generations requires a combination of in situ age dating and trace element geochemistry in petrogenetic context.

An introduction to Recent Advances in Understanding Gold Deposits: from Orogeny to Alluvium: the importance of multi-method approaches and developing a characterization

Abstract Gold occurs in many settings but the dynamic nature of Earth's crust means overlapping and overprinting deposit styles are common. Characterization of mineralization from an early stage becomes important particularly where the mineralization is complex, in order to maximize exploration and project development success, and mining productivity. Various techniques are used at different stages of a project to characterize gold deposits. This Special Publication Recent Advances in Understanding Gold Deposits: from Orogeny to Alluvium offers a cross-section of some specific techniques to investigate a variety of gold deposit types. In this Introduction, we briefly compare the most common gold deposit types, summarize the techniques used to investigate them and discuss some of the most important outstanding questions regarding understanding gold deposits. This is followed by a summary of each paper in this Special Publication. Whilst the 15 papers in this book can only showcase some of the many approaches available, they do highlight both the breadth of the available techniques and their utility in deposit characterization. Several papers include suggestions for avenues for fruitful further research, including a paper suggesting a new approach to classifying orogenic gold deposits, and a paper describing archaeological applications of natural gold analyses.

Occurrence State and Properties of Gold Minerals from the Gold Deposits on the North China Platform

By studying both the microscopic physical and chemical typomorphic characteristics of gold minerals associated with representative gold deposits on the north-central margin of the North China Platform, this paper seeks to identify macroscopic metallogenic mechanisms of gold deposits. The majority of the gold minerals from the gold deposits are native gold with minor electrum and calaverite. The form and grain size of gold minerals from the representative gold deposits reflect the metallogenic properties of medium-deep and medium-high temperature deposits. The projected gold fineness of the Xiaoyingpan gold mine all falls in the medium-temperature area in the figure and tends to be in the high-temperature area, while that of the Zhangquanzhuang gold mine mostly falls in the middle-temperature area, showing the difference in the metallogenic conditions of the two deposits. Both Xiaoyingpan and Zhangquanzhuang gold deposits show the following rules: poor in Zn, Pb, Sb and Se, but rich in Cu, Fe without Mn, indicating that both deposits are of medium-deep origin. The three representative gold deposits all show high gold fineness characteristics, and the general rules are as follows: Dongping-type gold deposit (934.8-969.7) > Xiaoyingpan-type gold deposit (900.0) > Zhangquanzhuang type gold deposit (824.0), showing that the representative gold deposits were formed at higher temperature and deeper depth, and the gold in the ores inherited the characteristics of high gold fineness originating from the Archean metamorphic rock series, which implying that the metallogenic material originated from the ancient metamorphic rock series; the long metallogenic period and multiple metallogenic stages made gold fully transformed, purified and enriched. There are three main occurrence states of gold minerals in the study area, from primary to secondary, they are respectively inclusion gold, gold minerals between other mineral crystals and those filled in the fractures of other minerals.

Studies of mineral composition of ores of the Kumtor deposit (Central Tien Shan) by QXRD and XRF nethods

Samples of various mineral ore types of the Kumtor gold deposit (Central Tien Shan) were studied using XRF method on a TORNADO M4 analyzer by digital processing of images of the elemental scanning maps to reveal the possibilities of this method to measure the mineral composition of ores without using the AMICS electronic mineral database. During the experimental work, the optimal parameters of elemental analysis and scanning of samples were selected, which allow maximum information with minimal time and expenses. The experimental analyses enabled us to estimate the semi-quantitative content of major ore-forming non-metallic and ore minerals and to establish the possible presence of minerals previously unknown in the composition of ores (barytocalcite, viterite, ferrinatrite, etc.). The macro- and microscopical identifcation of these minerals is problematic, although their relative content locally reaches several weight percents.

Studies of mineral composition of ores of the Kumtor deposit (Central Tien Shan) by QXRD and XRF methods

Samples of various mineral ore types of the Kumtor gold deposit (Central Tien Shan) were studied using XRF method on a TORNADO M4 analyzer by digital processing of images of the elemental scanning maps to reveal the possibilities of this method to measure the mineral composition of ores without using the AMICS electronic mineral database. During the experimental work, the optimal parameters of elemental analysis and scanning of samples were selected, which allow maximum information with minimal time and expenses. The experimental analyses enabled us to estimate the semi-quantitative content of major ore-forming non-metallic and ore minerals and to establish the possible presence of minerals previously unknown in the composition of ores (barytocalcite, viterite, ferrinatrite, etc.). The macro- and microscopical identifcation of these minerals is problematic, although their relative content locally reaches several weight percents.

Deep exploration of Jiaodong type gold deposit, taking Shanhou gold deposit, southern part of Zhaoping fault as an example

Crustal response induced by the subduction of Paleo-Pacific Plate, is crucial to study the metallogenic law and prediction of Jiaodong type gold deposit. Gold deposits are preferentially hosted in the lithospheric-scale second-order faults, which provide migration channels, mineralization corridors, and the physicochemical conditions. Super-large gold deposits in northwestern Jiaobei Terrane are generally controlled by regional linear faults, such as Sansandao, Jiaojia, Zhaoping and Qixia faults. However, Zhaoping fault is exposed sporadically (in Xiadian and Jiangjiayao gold deposits) beneath a thick cover of Quaternary basalts, which indicating that limited information can be obtained by traditional geological survey. In this study, high-precision geophysical surveys such as gravity and controlled source audio frequency magnetotellurics (CSAMT) are conducted in the Shanhou gold deposit, which hosted in southern part of Zhaoping fault. Three integrated geophysical profiles results further identified the spatial distribution of second-order oblique-slip faults of Zhaoping fault and established the relationships between brittle deformation and mineralization. The spatial variability of stratum (high density 2.82 g/cm3 and intermediate to high specific resistivity 4000 Ω m), brittle-slip faults (intermediate density 2.73 g/cm3 and low specific resistivity 200 Ω m) and magmatite (low density 2.57 g/cm3 high specific resistivity 8000 Ω m) are identified by two inversion techniques, including the man-machine interactive inversion technology and nonlinear conjugate gradient technology. In addition, the geophysical inversion pseudo sections delicately portray a smooth-out waveform low specific resistivity anomaly, which strongly couples with the spatial ore-hosted locations and enrichment places. The gold mineralized alteration zones generally dips to southeast and the angle changing from 45° to 30°, which are strong coupling with the large-scale acid magmatic intrusion and extensional tectonics occurred in the late Mesozoic. Finally, according to the deep prospecting prediction, a gold ore body with 10 m in thickness was revealed by drilling below the depth of 1,015 m, which is hosting in the brittle deformation of Zhaoping fracture zone.

The roles of hydrocarbons on the mineralization of Carlin-type gold deposits, Nanpanjiang Basin, South China

The spatial association of hydrocarbons with metalliferous ore deposits, like MVT lead–zinc deposits, sandstone uranium deposits and various type gold deposits (epithermal Au-Ag (-Hg) deposits, orogenic gold deposits and Carlin-type gold deposits) is found worldwide. However, the genetic relationship between hydrocarbon evolution and mineralization is still under controversy. Integrating isotope dates related to timing of petroleum evolution and gold mineralization from published data, as well as high-resolution transmission electron microscopy (TEM) analysis of pyrobitumen, electron probe microanalysis (EPMA) on both pyrobitumen and pyrite, the In-situ S isotope analyses of the gold-bearing pyrite in this study, we consider different type hydrocarbons (liquid oil and gas) played different roles on the mineralization of Carlin type gold deposits. As the residue of liquid oil cracking, the widespread high maturity pyrobitumen within the reservoir indicate both oil and gas has ever accumulated in the Nanpanjiang Basin. The high gold abundance (EPMA: ∼120 ppm; TEM: ∼1500 ppm) within the pyrobitumen in agreement with the metal solubility experiment suggest liquid oils could have acted as gold carrier before metal precipitation. The late Triassic timing overlapping between gas generation and gold mineralization and the δ34S features with gold bearing pyrite ∼ 10 ‰ lighter than the coeval seawater sulfate indicate gas dominated TSR process may play an important role on the supply of gold bisulfide complex (Au(HS)2−) in the ore-forming fluid and directly involved the precipitation of the Carlin-type gold deposit.

Fluid inclusion and in situ sulfur isotope studies of the carbonaceous strata-hosted Eryiling gold deposit in the Beishan orogen, NW China

The Eryiling gold deposit in the Jinwozi orefield is a carbonaceous strata-hosted gold deposit in the Beishan Orogen, NW China. The gold orebodies are mainly layered, lenticular, and vein hosted in Jinwozi Formation, different from the Jinwozi gold deposit. In this contribution, based on a comprehensive study including field investigation of ore geology, fluid inclusion microthermometry, and in situ sulfur isotopic composition, we discuss the origin and source of the ore fluids and the gold precipitation mechanism at the Eryiling deposit. The ore-forming process includes the early milky white quartz-pyrite vein, the main stage smokey gray quartz-sulfide vein, and the late-stage quartz-calcite vein. The auriferous vein characterizes the main-stage veins. By micro-thermometry, CO2-bearing(C-), Pure CO2(PC-), Water(W), and daughter crystal(S) types of fluid inclusions were identified and investigated. The early-stage quartz vein contains C-type FIs with a salinity of 3.5 to 7.7 wt% NaCl eqv., and total homogenization temperature (Th) of 243 and 321 °C. It shows that the ore fluids possess characters of low salinity, CO2-rich, and mesothermal. These characters resemble to those of orogenic-type gold deposits. The C-type FIs in the main stage quartz show salinity of 3.5 to 8.9 wt% NaCl eqv., and Th of 200 and 350 °C. The W-type FIs are coexisting with C-type FIs which they yield salinity of 5.5 to 10.2 wt% NaCl eqv., and Th of 158 – 287 °C. A large amount of immiscibility fluid inclusion assemblages found in the main stage quartz provide clear evidence for gold precipitation caused by fluid immiscibility. Trapping pressures of 61–233 MPa for the early stage and 48–182 MPa for the main stage are estimated, equivalent to mineralization depths of ∼ 8.1 km and ∼ 6.4 km, respectively. The δ34S value of sulfide increased from early-stage (average of 3.8 ‰) to main-stage (average of 6.4 ‰), indicating sulfur contributed by the wall rocks through fluid-rock interaction as the wall-rock sulfide display value of average of 16.2 ‰. In summary, the Eryiling gold deposit is situated in the altered carbonaceous rock of the Jinwozi Formation and regulated by a fractured zone, which could be considered a typical carbonaceous strata-bound orogenic gold deposit. Moreover, the similarity of ore-forming fluids between Jinwozi and Eryiling gold deposits indicates that they are the products of the same ore-forming fluid in different wall rocks.

Decompression induced enrichment and precipitation of gold in the polymetallic sulfide stage of the northwest Jiaodong gold deposits, eastern North China Craton

Mechanisms for the enrichment and re-precipitation of gold in the giant Jiaodong gold deposits (eastern North China Craton) remain poorly constrained. To better understand the mineralization mechanism, we did in situ analyses of S isotopes on sulfides such as pyrite, pyrrhotite, galena and chalcopyrite from the disseminated (altered-rock type) and quartz-vein type gold deposits by femtosecond laser ablation coupled multi-collector inductively coupled plasma mass spectrometry. Pyrites from the altered-rock type gold deposit show δ34S values in the range from 7.4 to 11.3 ‰, which is obviously heavier than the quartz-vein type gold deposits with δ34S = 6.2 ∼ 8.8 ‰. Traditionally, the difference of sulfur isotopic compositions between the two types of gold deposits was attributed to the change in oxygen fugacity. However, we found that, from early to late metallogenic stage, sulfur isotopes of pyrites from the altered rock type gold deposits tend to decrease gradually and pyrrhotites can always be observed in the third stage. Moreover, the S isotopic compositions (δ34S = 7.9 to 8.2 ‰) of the pyrites coexisting with magnetite are comparable with those (δ34S = 6.2 to 8.0 ‰) of the pyrites coexisting with pyrrhotite in the quartz vein type gold deposits. These features indicate that the decrease of sulfur isotopes in pyrites was not caused by increase of oxygen fugacity. We suggest that the S isotopic and fO2 variation could be ascribed to an increase of pH of the ore-forming fluid, which is supported by the typically quartz dissolution and common occurrence of calcite and pyrrhotite in the late metallogenic stage (the third stage) and an overall decrease of aluminum contents of quartz from core to rim. We further proposed that the variation of pH of ore-forming fluids is probably related to a process of decompression due to development and enlargement of fractures filled with ore-forming fluids. Gold enrichment in the main ore-forming stage of the northwest Jiaodong gold deposit probably was realized by multiple phases of fluid pressure fluctuation, which subsequently led to repeatedly dissolution and re-precipitation of Au from pyrites due to decreasing oxygen fugacity and increasing pH values of the ore-forming fluids.

LA-ICP-MS zircon U-Pb dating of granite porphyry and 40Ar/39Ar dating of chromian sericite of the Shuangqishan and Xiaoban gold deposits in central Fujian, South China and their restriction on gold mineralization

The shuangqishan and Xiaoban are the two largest gold deposits in the Dehua-Youxi-Yongtai (DYY) mineral concentrated area of central Fujian Province. They are located adjacent to each other and show similarities in geological background, metallogenic characteristics and mineral assemblage. The orebodies are hosted in the Caledonian alaskite and the metamorphic rock of Neoproterozoic Daling Formation. Gold mineralization is closely related to pyritization, silicification, and micatization, with native gold mostly occurring in the cracks of pyrite, which formed slightly later than pyrite. In this paper, geochronologic work has been conducted on the granite porphyry and chromian sericite related to gold mineralization in the two deposits to determine the age of mineralization and discuss the genesis of the deposits. The chromian sericite is a hydrothermal alteration product of granite porphyry, and is a main indicator of gold enrichment. The plateau 40Ar/39Ar isotopic dating of chromian sericite indicates the mineralization ages of the two deposits were 146.21 ± 1.59 Ma and 149.28 ± 1.26 Ma respectively, similar to the LA-ICP-MS zircon U-Pb age(149.0 ± 1.0 Ma) of granite porphyry in the mining district. The ages of the chromian sericite and granite porphyry point to a close link with a large-scale magmatism event at the late stage of Late Jurassic in central Fujian. Based on the geology, alteration, mineralization and chronology characteristics, the Shuangqishan and Xiaoban gold deposits can be classified as the magmatic hydrothermal type gold deposits.

Alteration and mineralization patterns in orogenic gold deposits: Constraints from deposit observation and thermodynamic modeling

Hydrothermal alteration and mineralization types of orogenic gold deposits display many variations depending on formation depths, types of host rock, compositions of ore fluids, spatial positions, fluid/rock ratios, and repetitive modifications during multiple fluid infiltrations in the complicated processes of fluid-rock interaction. Therefore, establishing holistic reference patterns of hydrothermal alteration with associated mineralization for the orogenic gold system is necessary. Based on the observation of typical orogenic gold deposits and thermodynamic simulation of fluid-rock reaction, the general features of proposed patterns include:(1)Orogenic ore fluids are capable of transporting sufficient gold from deep (5 kbar and 600°C) to shallow (1 kbar and 200°C) crustal levels, resulting in alteration and mineralization occurred in a much-varied depth. Only considering the effects of fluid-rock reaction and sulfidation, the formation of pyrrhotite and pyrite at relatively high and low P-T conditions, respectively, is the most important mechanism driving gold precipitation. In addition, the changes of fluid fO2 and pH can also trigger a decrease in the gold solubility in fluids.(2)Multiple waves of fluid infiltration are capable of dissolving the early-formedulfides and gold, and reprecipitate them in the distal alteration zones, which can explain the irregular gold concentration distribution patterns in wide alteration zones. The fluids under higher P-T conditions (5 kbar and 600°C and 3 kbar and 400°C) are more capable of dissolving early-formed sulfides and gold. Additionally, the later infiltrated fluids can transform early-formed pyrrhotite into pyrite.(3)The model of interactions between ore fluids and aluminosilicate rocks at varied P-T conditions indicates that the alteration mineral assemblages in hypozonal deposits (>12 km) mainly include biotite, amphibole, anorthite, K-feldspar, quartz, and pyrrhotite assemblages; that those in mesozonal deposits (6 to 12 km) are characterized by chlorite, calcite, quartz, muscovite, pyrite or pyrrhotite. The epizonal deposits (<6 km) commonly develop more abundant Fe-Mg bearing carbonates (e.g., dolomite, ankerite, and siderite), quartz, muscovite, and pyrite. The compositional variations of ore fluids and host rocks have important controls on the development of iron-oxides and carbonaceous material.(4) The alteration halo is relatively restricted under hypozonal to lower mesozonal conditions. However, broad carbonation develops under upper mesozonal to epizonal conditions, with Fe-Mg bearing carbonates and calcite distributed in proximal and distal zones, respectively.

Typomorphism of Native Gold (Geological-Industrial Types of Gold Deposits in the North-East of Russia)

This study presents the typomorphic features of native gold grains from three different geological-industrial types (GIT) of gold deposits in the North-East of Russia: (1) gold–arsenic-sulfide in black shale strata (Natalka, Degdekan, Karalveem, Maldyak deposits), (2) gold–quartz veins in granitoids (Dorozhnoye, Butarnoye, Shkolnoye, Maltan deposits), and (3) gold–silver adularia in volcanogenic strata (Kupol, Olcha, Kubaka, Burgali, Primorskoe, Dalnee deposits). The reliability of the geological interpretation is directly related to mineral associations, fineness variations, its internal structure and the content of microimpurities. Native gold is a reliable indicator for identifying various GIT of gold deposits at the early geological-prospecting stages of studying gold-bearing areas. Typomorphic features of native gold for each of the considered GIT are stable and do not depend on the age and scale of mineralization. It is shown that using an integrated approach obtains genetic information about a particular ore object, which makes it possible to predict the vertical range of mineralization and outline the technology for processing ores. The information obtained can also be effectively used in the search for placer deposits in nearby watercourses. Identification of typomorphic features of ore and placer native gold opens up wide opportunities for delineating the distribution areas of placer deposits.