Geology Of Deposits Research Articles

Geology, geochemistry and tectonic settings of molybdenum deposits in Southwest China: A review

Southwest (SW) China hosts more than 26 Mo (Mo-only, Mo-dominated and Mo-bearing) deposits with a total reserve of >2.5Mt Mo metal. The region has become one of the most important Mo mineral provinces in China. These Mo deposits are usually fault-controlled, and are located mainly in: (1) Lhasa Terrane, characterized by widely distributed Yanshanian–Himalayan igneous rocks; (2) Qiangtang Terrane, composed by Proterozoic and Early-Paleozoic crystalline basement and Devonian to Jurassic cover rocks; (3) East Kunlun Terrane, comprising Precambrian metamorphic rocks intruded by Paleozoic and Mesozoic granitoid plutons; (4) West Kunlun Terrane, characterized by Precambrian metamorphic basement, Paleozoic metasedimentary rocks, and Early-Paleozoic and Carboniferous–Triassic arc-type plutons; and (5) Yidun arc, composed by Middle and Upper Triassic volcanic–sedimentary successions. The Mo mineralization styles are dominated by porphyry-type, but also contain porphyry-skarn, skarn and porphyry-quartz vein types. Orebodies are vein-type or lensoidal, and are hosted by a variety of metamorphic, volcanic, granitic and sedimentary rocks of different ages. Fluid-rock interactions are exemplified by alteration zonation, which usually grades from an innermost potassic alteration zone, via a silicic/sericite alteration zone, to an outermost propylitic alteration zone. The initial high-temperature ore-forming fluids are magmatic in origin, and contain CO2-bearing fluid inclusions. The initial ore-forming fluids would have then evolved to low-temperature, low-pressure, low-salinity and CO2-poor (with meteoric water input) at the late alteration/mineralization stage. Causative granitoids for these Mo deposits have relatively high SiO2, K2O and Al2O3, and low TiO2 and MgO, showing a metaluminous to peraluminous high-K calc-alkaline to shoshonitic affinity. These granitoids exhibit significant depletions in Ba, Nb, Ta, P and Ti, and enrichments in Rb, Th, U and K. It is suggested that they were originated from partial melting of a lower rejuvenated crust, as evidenced by their Sr-Nd-Pb isotopic signatures. The Mo deposits in East and West Kunlun were formed in the Triassic (ca. 258–214Ma), related to the Paleo-Tethys Ocean subduction and the subsequent continental collision. Major Mo mineralization in the Qiangtang and Lhasa terranes mainly occurred during the syn-collisional compression to post-collisional extension transition of the Qiangtang–Lhasa (ca. 43–35Ma) and India–Asia (ca. 30–14Ma) collisions, respectively. The Late-Cretaceous Mo mineralization (ca. 88–73Ma) in the Yidun arc was formed during the late- or post- Lhasa–Qiangtang collision setting, or the intraplate extension led by the post-Himalayan escape tectonics. The wide range of molybdenite Re contents in these major SW Chinese Mo deposits indicates remarkable differences in metal, fluid sources and ages.

Michel Cuney and Kurt Kyser: Geology and Geochemistry of Uranium and Thorium Deposits

Michel Cuney and Kurt Kyser: Geology and Geochemistry of Uranium and Thorium Deposits

Mineralization age and geodynamic background for the Shangjiazhuang Mo deposit in the Jiaodong gold province, China

The Shangjiazhuang Mo deposit is located on the Jiaodong Peninsula in eastern China, which is famous for the ca. 120Ma “Jiaodong-type” Au deposits with total Au endowment of over 3000t. In this paper, we discuss the deposit geology, mineralization age, and geochemical features of the host granodiorite of the Shangjiazhuang Mo orebody. Using this information, we aim to clarify the time and geodynamic mechanism for the Mo deposit, which is another constraint to understand the genesis of Au deposits. The Mo mineralization generally occurs as quartz–sulfide veins within the medium-grained Yashan granodiorite. The alteration consists of potassic alteration, silicification, sericitization, chloritization, and carbonatization with a weak unclear zonation. The ore minerals mainly include molybdenite, chalcopyrite, and pyrite. We measured Re–Os isotopes of molybdenite grains, which yielded a weighted mean model age of 116.9±0.81 (MSWD=1.03) and a well-constrained 187Re–187Os isochron age of 117.1±1.4Ma (MSWD=1.6). These ages are slightly younger than the age of Au mineralization on the Jiaodong Peninsula. Rhenium contents of 5.84–29.99ppm with an average of 16.4ppm in molybdenites indicate a crustal source. Whole-rock geochemical compositions show that the granodiorite is high-K calc-alkaline and metaluminous to peraluminous. The samples show low Y contents from 8.2 to 10.5ppm and Sr/Y ratios from 48.2 to 58.8, displaying an adakitic affinity. The Yashan granodiorite has high initial 87Sr/86Sr ratios of 0.7101 to 0.7104, low εNd(t) values of −17.6 to −16.7, and zircon εHf(t) values from −24.8 to −17.1, with corresponding Hf model ages of 2.7 to 2.2Ga. These isotopic data, together with the adakitic affinity of the granodiorite, indicate that the parental magma was derived from ancient crust. Mafic microgranular enclaves (MME) that are contemporaneous with the host granodiorite show SiO2 contents of 57.98–58.41wt% and depletion in Nb–Ta. The MMEs show enriched initial 87Sr/86Sr ratios of 0.7102 to 0.7106 and low εNd(t) values of −17.3 to −16.3. The MMEs are the products of mixing between the metasomatized lithospheric mantle-derived mafic magma and the ancient crust-derived felsic magma. The Early Cretaceous Mo mineralization (120–110Ma) is slightly younger than the peak time of Au mineralization (126–120Ma) on the Jiaodong Peninsula, but have a different spatial distribution which suggests different sources of Au and Mo. The “Jiaodong-type” Au deposits were probably related to the upwelling of metasomatized lithospheric mantle, while the Mo mineralization on the Jiaodong Peninsula may delineate a 120–110Ma Mo metallogenic belt along the southern margin of the North China Craton with the East Qinling, which is related to the melting of ancient crustal sources. The subduction of the Paleo-Pacific slab and accompanying asthenospheric upwelling triggered upwelling of metasomatized lithospheric mantle, forming “Jiaodong-type” Au deposits. Subsequently, the ponding of mantle-derived magmas resulted in partial melting of ancient crust and associated Mo deposits.

Controls on the distribution of deep‐sea sediments

AbstractDeep‐sea sediments represent the largest geological deposit on Earth and provide a record of our planet's response to conditions at the sea surface from where the bulk of material originates. We use a machine learning method to analyze how the distribution of 14,400 deep‐sea sediment sample lithologies is connected to bathymetry and surface oceanographic parameters. Our probabilistic Gaussian process classifier shows that the geographic occurrence of five major lithologies in the world's ocean can be predicted using just three parameters. Sea‐surface salinity and temperature provide a major control for the growth and composition of plankton and specific ranges are also associated with the influx of non‐aerosol terrigenous material into the ocean, while bathymetry is an important parameter for discriminating the occurrence of calcareous sediment, clay and coarse lithogenous sediment from each other. We find that calcareous and siliceous oozes are not linked to high surface productivity. Diatom and radiolarian oozes are associated with low salinities at the surface but with discrete ranges of temperatures, reflecting the diversity of planktonic species in different climatic zones. Biosiliceous sediments cannot be used to infer paleodepth, but are good indicators of paleotemperature and paleosalinity. Our analysis provides a new framework for constraining paleosurface ocean environments from the geological record of deep‐sea sediments. It shows that small shifts in salinity and temperature significantly affect the lithology of seafloor sediment. As deep‐sea sediments represent the largest carbon sink on Earth these shifts need to be considered in the context of global ocean warming.

A Research Review of Iron Oxide Copper‐Gold Deposits

AbstractIron oxide copper‐gold (IOCG) deposits are a research focus of the current ore deposit geology, and have attracted much attention among the worldwide geologists and exploration experts due to their shallow depth, a wide variety of mineral species and large scale. This paper presents a review of the present IOCG deposits research, which includes the definition of IOCG deposits, temporal and spatial distribution, ore‐forming environments, ore‐forming magmatic rocks, their geological features, ore‐controlling structures and ore‐bearing rocks, mineralized alteration zoning, and their genesis and ore‐forming process. This work also proposed the ore prospecting direction of IOCG deposits from a trinity model of metallogenic geological bodies, metallogenic structure surface and metallogenic information signs, and discussed the existing problems of the IOCG deposits research.

Geological and Exploration Models of Beach Placer Deposits, Integrated from Case-Studies of Southern Australia

The processes leading to the formation of beach placer deposits generally begin inland and terminate at the coast, including source rocks being weathered, eroded and then transported by streams and rivers to the coast, where the sediments are deposited in a variety of coastal environments. The coastal sediments are reworked by the action of waves, tides, longshore currents and wind, which are effective processes for sorting the mineral grains based on differences in their size and density, resulting in laminated or lens-shaped packages of sediments up to tens of meters thick that are rich in heavy minerals. Detailed studies of sedimentary basins, as well as peripheral (paleo-)valleys that drained sediment source areas, are important tools in the exploration for heavy mineral resources. Knowledge of the (paleo-)basin, associated valley architecture and the source of heavy minerals concentrated in the shorelines and valleys are useful guides to the potential for, and location of, economic deposits.Evidence from sedimentology can be combined with that from other geological and geophysical characteristics to arrive at a general reconstruction of basin and paleovalley architecture and depositional environments. Complex paleogeography of the shorelines can influence or determine the sites of heavy mineral concentration. Heavy mineral sands tend to concentrate in certain shoreline settings during storm activity. Repeated storm erosion and reworking over centuries (e.g., the southeastern coast of Australia) or millennia (e.g., the Eucla and Murray Basins of Australia) can progressively enrich heavy mineral sand deposits. Preservation of these deposits over a geological timeframe of millions of years can ensue through subsidence of coastal sediments, and during sea-level change that results in either shorelines migrating inland (marine transgression) or seaward (marine regression), potentially burying or stranding earlier deposits or reworking them to form younger deposits. Refinements in remote sensing and geophysical techniques, data processing, sedimentology and computer-aided interpretations provide effective, economic and efficient methods for modeling coastal reconstructions and for exploring provinces and terrains prospective for heavy mineral sand deposits. Landscape topography analysis, combined with geophysical methods that can resolve physical property contrasts between the shoreline sediments and underlying sequences, are increasingly used in mineral exploration to locate and to reconstruct paleoshorelines and paleovalleys.Australia has modern and ancient beach-placer deposits, both of which show many similar geologic features. The formation of these heavy mineral deposits provides one of the best examples of applying knowledge of modern systems (e.g., the west and east coasts of Australia) as an analogue to interpret and understand the geology and form of ancient deposits (e.g., the Eucla and Murray Basins of southern Australia). This study provides descriptive and exploration models of Australia’s heavy mineral sand deposits formed in coastal environments, which can be applied to similar settings worldwide.

Thermodynamic efficiency of carbon capture and utilisation in anaerobic batch digestion process

Carbon capture and storage (CCS) in the oil and water industries is becoming common and a significant consumer of energy typically requiring 150–450°C and or several hundred bar pressure [1] particularly in geological deposition. A biological carbon capture and conversion has been considered in conventional anaerobic digestion processes. The process has been utilised in biological mixed culture, where acetoclastic bacteria and hydrogenophilic methanogens play a major key role in the utilisation of carbon dioxide. However, the bio catalytic microorganisms, hydrogenophilic methanogens are reported to be unstable with acetoclastic bacteria. In this work the biochemical thermodynamic efficiency was investigated for the stabilisation of the microbial process in carbon capture and utilisation. The authors observed that a thermodynamic efficiency of biological carbon capture and utilisation (BCCU) had 32% of overall reduction in yield of carbon dioxide with complimentary increase of 30% in yield of methane, while the process was overall endothermic. Total consumption of energy (≈0.33MJl−1) was estimated for the carbonate solubility (0.1moll−1) in batched BCCU. This has a major influence on microbial composition in the bioreactor. This thermodynamic study is an essential tool to aid the understanding of the interactions between operating parameters and the mixed microbial culture.

Geology of the PQ deposit, Sri Lanka

The PQ heavy mineral sand deposit is located on the west coast of Sri Lanka, approximately 30 km north of the town of Puttalam within the North Western Province. The PQ heavy mineral deposit was previously defined and explored between 1994 and 2002. Since 2010 further evaluation work has been completed. The ilmenite dominated deposit is hosted in a Quaternary to Recent age sedimentary sequence overlying the Miocene Vanathavillu limestone. It is a relatively homogenous red-brown palaeo-dunal deposit that extends for more than 5 km in length, is up to 3-km wide and contains 46.4 Mt of heavy mineral. Mineralisation commences from surface to a depth of over 50 m and grades range between 1.0 and 50.4% total heavy minerals. The PQ deposit shares many similar attributes with the teri sand (red sands) environments in southern India in terms of size, increased heavy mineral concentration, depositional environment and age.

Adsorption-desorption behavior of dissolved organic carbon by soil clay fractions of varying mineralogy

Soil clay minerals significantly influence the accumulation and stabilization of organic carbon (OC). However, the effect of interactions among phyllosilicate clay minerals, native OC and sesquioxides (Fe/Al oxides) on the adsorption-desorption of dissolved organic carbon (DOC) under different background electrolyte types and concentration is poorly understood. A set of batch adsorption-desorption experiments were conducted using pedogenic clays extracted from soils dominated by kaolinite-illite (Kaol-Ill), smectite (Smec) and allophane (Allo). The clay samples were sequentially treated to remove native OC and sesquioxides, and tested for adsorption-desorption of DOC under various solution conditions. All the experiments were conducted at pH7 using water extractable fraction of OC from wheat residues. DOC adsorption increased with increasing background electrolyte concentration, and the presence of Ca2+ significantly enhanced the uptake in comparison to Na+ due to a possible cationic bridging effect. Under all electrolyte conditions, the maximum DOC adsorption capacity (Qmax) (mgg−1) of the soil clay fractions (SCF) maintained the order: Allo>Smec>Kaol-Ill. A similar order was also observed when the adsorption capacities were normalized to the specific surface area (SSA) of the SCFs (mgm−2). DOC adsorption showed a positive relationship with SSA, and sesquioxides and allophanic minerals provided the largest contributions to the SSA in the SCF. Removal of sesquioxides from the SCF resulted in a decrease in SSA and thus DOC adsorption, whereas removal of native OC increased the SSA and subsequent DOC adsorption. Because this study used pedogenic SCFs which represented soils formed in different environments instead of processed clays from geological deposits, it provided realistic information about the interaction of DOC with SCF in relation to their native OC and sesquioxide contents. It also revealed the importance of Ca2+ in enhancing the carbon adsorption capacities of these SCFs.

A Historical Sketch of the Landscape of the Red River Delta

AbstractThis article is an attempt to stand back and re-imagine the landscape of the Red River over the last two millennia. The only static components of the Red River valley and delta are its mountains and geological deposits, everything else has changed over time. By marrying historical records with recent scientific findings on the Red River, this article outlines aspects of these changes; including changes to the climate and landscape, the possibility of shifting river courses, the movement of historical trade routes, and the rise of Thang Long–Hanoi.

Value from legacy data

In the mining industry, legacy hardcopy and digital exploration data are central to due diligence for mergers and acquisitions, and are the basis for planning future exploration programmes. Alpha-numeric data may be checked algorithmically for consistency and obvious errors. This is essential, but misses the critical understanding and confirmation that comes from field validation, the re-collection of data and their rigorous use in (re)interpreting deposit geology. Data rescue and validation are precursors to data up-cycling with the over-arching aim being the construction of a 3D model matching geology and grades. This paper comments on todays’ trends in data management, using a recent case study where digital and non-digital data were used in combination with new techniques and technologies to identify the fourth-largest tungsten Resource (with JORC-code compliant announcement). This was achieved without direct drilling costs, making it perhaps one of the cheapest Resource announcements ever. Importantly, none of this could have been achieved by office-bound data inspection or translation.

Applying multivariate statistics to discriminate uranium ore concentrate geolocations using (radio)chemical data in support of nuclear forensic investigations

The application of Principal Components Analysis (PCA) to U and Th series gamma spectrometry data provides a discriminatory tool to help determine the provenance of illicitly recovered uranium ore concentrates (UOCs). The PCA is applied to a database of radiometric signatures from 19 historic UOCs from Australia, Canada, and the USA representing many uranium geological deposits. In this study a key process to obtain accurate radiometric data (gamma and alpha) is to digest the U-ores and UOCs using a lithium tetraborate fusion. Six UOCs from the same sample set were analysed ‘blind’ and compared against the database to identify their geolocation. These UOCs were all accurately linked to their correct geolocations which can aid the forensic laboratory in determining which further analytical techniques should be used to improve the confidence of the particular location.

Global occurrence, geology and characteristics of tubular halloysite deposits

AbstractHalloysite with tubular morphology is formed in a wide range of geological environments from the alteration of various rock types. Intrusive acidic coarse-grained rocks, such as granites, pegmatites and anorthosite, with large potash and sodic feldspars contents, are subsequently altered to kaolinite, halloysite and other clay minerals by weathering or shallow hydrothermal fluid activity. Processing to separate the halloysite-kaolinite fraction from the altered host rock provides a product which can be used as a paper filler and in ceramics and fibreglass, among other uses, with various deposits in Brazil, China, Thailand and elsewhere. In the Kerikeri-Matauri Bay district of Northland, North Island, New Zealand, volcanic alkali rhyolite was extruded as domes and cooled rapidly with fine-grained feldspar subsequently altered to halloysite. The IMERYS plant in Matauri Bay separates the clay from the quartz-cristobalite matrix with an ∼20% yield of halloysite. The principal market is for high-quality porcelain and bone china that require low levels of Fe2O3 and TiO2. Deposits with high levels of halloysite occur in China, Turkey and the USA. The Dragon mine in Utah, USAwas recently reopened by Applied Minerals Inc. and now produces halloysite from zones of up to 100% white halloysite. Smaller occurrences of tubular halloysite are mined in China, Turkey and elsewhere from masses of comparatively pure clay that appear to have crystallized directly from solutions in which Al and Si were soluble.

Geology, Fluid Inclusion and Isotopic Study of the Neoproterozoic Suoi Thau Copper Deposit, Northwest Vietnam

AbstractThe Sin Quyen‐Lung Po district is an important Cu metallogenic province in Vietnam, but there are few temporal and genetic constraints on deposits from this belt. Suoi Thau is one of the representative Cu deposits associated with granitic intrusion. The deposit consists of ore bodies in altered granite or along the contact zone between granite and Proterozoic meta‐sedimentary rocks. The Cu‐bearing intrusion is sub‐alkaline I‐type granite. It has a zircon U‐Pb age of ∼776 Ma, and has subduction‐related geochemical signatures. Geochemical analysis reveals that the intrusion may be formed by melting of mafic lower crust in a subduction regime. Three stages of alteration and mineralization are identified in the Suoi Thau deposit, i.e., potassic alteration; silicification and Cu mineralization; and phyllic alteration. Two‐phase aqueous fluid inclusions in quartz from silicification stage show wide ranges of homogenization temperatures (140–383°C) and salinities (4.18wt%–19.13wt%). The high temperature and high salinity natures of some inclusions are consistent with a magmatic derivation of the fluids, which is also supported by the H‐O‐S isotopes. Fluids in quartz have δD values of −41.9‰ to −68.8‰. The fluids in isotopic equilibrium with quartz have δ18O values ranging from 7.9‰ to 9.2‰. These values are just plotted in the compositional field of magmatic‐hydrothermal fluids in the δDwater versus δ18Owater diagram. Sulfide minerals have relatively uniform δ34S values from 1.84‰ to 3.57‰, which is supportive of a magmatic derivation of sulfur. The fluid inclusions with relatively low temperatures and salinities most probably represent variably cooled magmatic‐hydrothermal fluids. The magmatic derivation of fluids and the close spatial relationship between Cu ore bodies and intrusion suggest that the Cu mineralization most likely had a genetic association with granite. The Suoi Thau deposit, together with other deposits in the region, may define a Neoproterozoic subduction‐related ore‐forming belt.

Geology and geochemistry of the Huilvshan gold deposit, Xinjiang, China: Implications for mechanism of gold precipitation

The Huilvshan gold deposit in the west Junggar (Xinjiang, China) is hosted in chloritized basalts, chlorite–siderite-altered basalts, and quartz–siderite rocks. Our study demonstrated that all these rocks were derived by alteration of basalts in a shear zone. The orebodies, consisting of quartz-sulfide veins and disseminated sulfides, formed in five stages: quartz–muscovite (I), disseminated sulfides (II), quartz–ankerite-sulfide (III), quartz–calcite-sulfide (IV), and quartz–calcite (V). Auriferous minerals are native gold in stage III and electrum in stage IV. During alteration of basalts in the shear zone, ore-forming elements were released from basalts to ore-forming fluid. Compared with fresh basalts, sulfide-bearing chloritized basalts contain much higher Sr, Ba, P, La, Ce, U, Mn, Ni, Zn, As, Ag, and Au contents. Phase analysis of the As–Cu–Fe–S–O system with the SUPCRT92 software package indicates that a decrease of the aH2S value, caused by the fluid–rock reactions and crystallization of sulfides, induced gold precipitation.

Geology, mineralogy and geochemistry of Pleistocene-Holocene deposits in the Çiftlik Basin (Niğde) (Central Turkey)

Geology, mineralogy and geochemistry of Pleistocene-Holocene deposits in the Çiftlik Basin (Niğde) (Central Turkey)

Delineation of Prospecting Zones of Groundwater Using Remote Sensing and Geographic Information System (GIS): A case Study of Solani River Basin

Initial delineation of prospecting zones of groundwater was conducted in the present study using remote sensing and geographic information system (GIS) techniques. It has been preparing an integrated geographic database of spatial and non-spatial data for the study area. The spatial data were generated by using image processing software (Erdas 8.3) and GIS software (Arc view 3.3) enhanced by real frequent field visits of the study area. These data include: surface features which give a direct and indirect indicators of the existence of groundwater and affect to the groundwater movement such as hydrogeomorphological, drainage density, slope, landuse and soil maps. The non spatial data were derived primarily from real views during field visits to the study area and from the existing writing or previous studies. All the data generated were saved in the GIS databank for the purpose of digitization, computational and generate the best possible output results to determine the extent of possible areas where the water that exists for the purpose of prospecting. Results showed that more areas could be have very good categories of prospect zones are the southern parts of the study area, which covers about 375 Km2 while the northern areas, which covers about 164 Km2 of the study area are grouped as runoff zone. Accordingly the possibilities of the presence of groundwater are poor to negligible in this zone. The current study demonstrated that a remote sensing and GIS technique are very effective tools that can give the initial predictions on the presence or probability of the presence of ground water in areas which have the same considered geological deposits for the study area.

Geology, ore facies and sulfur isotopes geochemistry of the Nudeh Besshi-type volcanogenic massive sulfide deposit, southwest Sabzevar basin, Iran

The southwest Sabzevar basin is placed in the southwestern part of a crustal domain known as the Sabzevar zone, at the north of Central Iranian microcontinent. This basin hosts abundant mineral deposits; particularly of the Mn exhalative and Cu-Zn volcanogenic massive sulfide (VMS) types. The evolution of this basin is governed by the Neo-tethys oceanic crust subduction beneath the Central Iranian microcontinent and by the resulting continental arc (Sanandaj-Sirjan) and back-arc (Sabzevar-Naien). This evolution followed two major sequences: (I) Lower Late Cretaceous Volcano-Sedimentary Sequence (LLCVSS), which is indicated by fine-grained siliciclastic sediments, gray basic coarse-grained different pyroclastic rocks and bimodal volcanism. During this stage, tuff-hosted stratiform, exhalative Mn deposits (Nudeh, Benesbourd, Ferizy and Goft), oxide Cu deposits (Garab and Ferizy) and Cu-Zn VMS (Nudeh, Chun and Lala) deposits formed. (II) Upper Late Cretaceous Sedimentary Dominated Sequence (ULCSS), including pelagic limestone, marly tuff, silty limestone and marl with minor andesitic tuff rocks. The economically most important Mn (Zakeri and Cheshmeh-sefid) deposits of Sabzevar zone occur within the marly tuff of this sequence. The Nudeh Cu–Zn volcanogenic massive sulfide (VMS) deposit is situated in the LLCVSS. The host-rock of deposits consists of alkali olivine basalt flow and tuffaceous silty sandstone. Mineralization occurs as stratiform blanket-like and tabular orebodies. Based on ore body structure, mineralogy, and ore fabric, we recognize three different ore facies in the Nudeh deposit: (1) a stringer zone, consisting of a discordant mineralization of sulfides forming a stockwork of sulfide-bearing quartz veins cutting the footwall volcano-sedimentary rocks; (2) a massive ore, consisting of massive replacement pyrite, chalcopyrite, sphalerite and Friedrichite with magnetite; (3) bedded ore, with laminated to disseminated pyrite, and chalcopyrite. Chloritization, silicification, sericitization and epidotization are the main wall-rock alterations; alteration intensity increases towards the stringer zone. The δ34S composition of the sulfides ranges from −1.5‰ to +3.69‰ with a general increase of δ34S ratios of massive ore facies to stockwork zone. The heavier values indicate that some of the sulfur was derived from seawater sulfate that was ultimately thermochemically reduced in deep hydrothermal reaction zones. Sulfur isotopes, along with sedimentological, textural, petrological, mineralogical, and geochemical evidences, suggest that this deposit should be classified as a Besshi-type VMS ore deposit.

Geology, geochemistry and tectonic settings of the molybdenum deposits in South China: A review

South China Block (SCB) is the area including the Yangtze Craton and the Huanan Orogen where scattered Precambrian terranes are usually regarded as segments of Cathaysia Land. It is the third most important molybdenum metallogenic province in China, next to the Qinling-Dabie area and Northeast China, containing 29 Mo-only or Mo-dominated, 9W-Mo(-Sn-Bi) and 8 Cu-Mo deposits. These 46 deposits are located mainly in: (1) the Lower Yangtze River Belt of the northeastern Yangtze Craton, (2) the Northern Jiangnan Orogenic Belt that is generally considered a Meso-Neoproterozoic magmatic arc complex accreted onto the southeastern margin of the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt characterized by local exposures of Proterozoic metamorphic terranes and the more widespread Sinian (Uppermost Proterozoic) to Triassic sedimentary sequences, and (4) the Southeast Coastal Volcanic Belt characterized by Yanshanian andesitic to felsic volcanic rocks. Their genetic types are dominated by porphyry and skarn mineral systems, with only a few quartz-vein systems. The orebodies form veins, lens, cylindrical shapes, pipes, or irregular in shape, usually controlled by faults at various scales and volcanic-subvolcanic complexes. The host-rocks are variable in lithologies, including granites, porphyries, volcanic breccias and tuffs, clastic sediments and carbonate rocks, but the high-grade orebodies are usually hosted in carbonate-shale sequences. Hydrothermal mineralization processes can be generally divided into four stages, from early to late, they are (1) K-feldspar-quartz veins or veinlets, (2) quartz-molybdenite stockworks, (3) quartz-polymetallic sulfide stockworks, and (4) quartz-carbonate-fluorite veinlets. Fluid-rock interaction as exemplified by wallrock alteration evolved from K-silicate alteration (K-feldspar-quartz-mica), through phyllic (quartz-sericite-chlorite-epidote), to propylitic or argillic alteration, with skarn alteration typically occurring in skarn-type mineral systems. Hydrothermal mineral assemblages vary between two end-members, namely the dry system formed by CO2-rich fluids and marked by quartz, K-feldspar, fluorite, carbonate and epidote, and the wet system mainly originated from CO2-poor fluids and composed of biotite, sericite and chlorite. The ore-forming fluids are magmatic in origin and show high-temperature and high-salinity. The melt-fluid systems forming Cu-Mo deposits are more oxidizing than those forming the W-Mo or Mo deposits, as suggested by accessory minerals in granitoids and daughter minerals in fluid inclusions. The Cu-Mo deposits are related to the I-type granitic rocks (adakite-like), whereas the W-Mo and Mo-only systems are related to granitic rocks of S- or A-types, although all of them show high K contents. Available isotope ages show that the Mo and Mo-bearing deposits were predominantly formed in the early Yanshanian Orogeny (170–134Ma), followed by the late Yanshanian Orogeny (110–92Ma) and the Caledonian Orogeny (450–410Ma). The Caledonian Mo-mineralization has been observed only in the Wuyi-Yunkai Orogenic Belt and related to the collision between the Yangtze Craton and the pre-Devonian Huanan Orogen or terranes separated from the Cathaysia Land, linked to the assembly of the Gondwana supercontinent. The Early Yanshanian mineralization affected the entire Huanan Orogen and the eastern Yangtze Craton, and resulted from the syn- to post-collisional tectonism following the closure of eastern Paleo-Tethys. The Late Yanshanian Mo deposits mainly occur in the Southeast Coastal Volcanic Belt and the southeastern margin of the Wuyi-Yunkai Orogenic Belt, and are related to the westward subduction of the Paleo-Pacific plate. The skarn-type mineral systems generally show lower Re contents than the porphyry-type deposits in a same tectonic unit, suggesting that carbonate host-rocks have lower Re contents than the causative porphyries. The Re contents in molybdenites from porphyry or porphyry-skarn Cu-Mo systems are >50ppm, mainly >100ppm, suggesting a source significantly contributed by the mantle; whereas the Re contents in molybdenites from the Mo-only or W-Mo-dominated deposits are <100pm, mainly <50ppm, indicating a genetic relation to the crust-sourced granitic magmatism.

Targeted Geoscience Initiative 4: Contributions to the Understanding of Precambrian Lode Gold Deposits and Implications for Exploration (B. Dubé and P. Mercier-Langevin, eds.)

Targeted Geoscience Initiative 4: Contributions to the Understanding of Precambrian Lode Gold Deposits and Implications for Exploration. B. Dube, P. Mercier-Langevin, editors. Geological Survey of Canada, Quebec. Open File 7852. 297 p. doi:10.4095/296624. This publication is available for free download through GEOSCAN (http://geoscan.nrcan.gc.ca/). Maybe I am just growing more skeptical in my old age, but much of what I read these days on gold deposits tends to rehash material that we have known for years. Other research commonly focuses on new data collected by state-of-the-art instrumentation that does little to address key issues to better aid our understanding of the economic geology of gold. This new volume on Canadian Precambrian gold deposits, however, represents a welcome contribution to our science that contains an exceptional amount of important new material on the geology and genesis of lode gold deposits. It is perhaps the most significant volume on the geology of gold published during the past decade. The papers in this well-edited volume summarize numerous studies conducted by Geological Survey of Canada geologists and their many collaborators as part of the TGI-4 research program carried out between 2010 and 2015. The opening paper, by Dube et al., summarizes many of the key findings of the major research themes of the project (BIF-hosted gold, intrusion-related gold deposits, and kinematics of crustal-scale faults) and discusses the resulting exploration implications. The progression—from relatively early formed auriferous VMS deposits, through synvolcanic intrusion-related deposits, and on to youngest BIF-hosted, classic quartz-carbonate vein-type, and other intrusion-related deposits—is well illustrated for key deposits in Quebec, Ontario, Nunavut, and Manitoba. A diversity in deposit styles is emphasized for the Superior Province, which is critical for geologists in planning their exploration strategies. …