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Actively mined Carlin-type gold provinces are only found in Nevada, USA, and SW China. Herein, we combined nanoscale secondary ion mass spectrometry and atom probe tomography to characterize the distribution of Au and As in pyrite from the micrometer to atomic scales from the Shuiyindong and Lannigou deposits, SW China, and compared this with a representative Nevadan deposit. Results show that invisible gold in both deposits occurs in complex micrometer and nanometer scale zones in the rims of pyrite. Within these oscillatory zones, Au is homogenously distributed rather than occurring as nanoclusters. This confirms that invisible gold is principally structure-bound Au, and that ore fluids were not saturated in Au. Gold deposition from undersaturated, arsenic containing, and ore fluids led to the formation of the giant Carlin-type gold deposits. Although not all high-As zones in the Lannigou pyrite contain high Au, all high-Au zones in both deposits contain elevated As. Arsenic is an important criterion for the incorporation of Au, but just because the fluid had high As does not necessarily imply it had/precipitated a high-Au pyrite. Gold atoms, in the Au–As rich zones of pyrite from both deposits, are surrounded by elevated concentrations of As compared to the matrix. Therefore, As both promotes Au incorporation into the pyrite and controls the maximum amount of structure-bound Au in the pyrite. Comparison of the Guizhou pyrite with Nevada pyrite reflects that the pyrite from the two districts exhibits the consistent nanometer- to atomic-scale characteristics. These similar nanometer- to atomic-scale characteristics further support the Guizhou deposits being classed as "Carlin-type." [ABSTRACT FROM AUTHOR]

Southwestern Guizhou province is one of China's most important distribution areas of Carlin-type gold deposits. The Nibao deposit is a typical gold deposit in southwestern Guizhou. To elucidate the genesis of the Nibao gold deposit, establish a metallogenic model, and guide prospecting prediction, we systematically collected previously reported geological, geochemical, and dating data and discussed the genesis of the Nibao gold deposit, based on which we proposed the metallogenic model. Earlier works show that the Nibao anticline, F1 fault, and its hanging wall dragged anticline (Erlongqiangbao anticline) were formed before or simultaneously with gold mineralization, while F2, F3, and F4 faults postdate gold mineralization. Regional geophysical data showed extensive low resistivity anomaly areas near the SBT (the product of tectonic slippage and hydrothermal alteration) between the P2/P3 and the strata of the Longtan Formation in the SSE direction of Nibao anticline in the lower plate of F1 and hanging wall dragged anticline (Erlongqiangbao anticline), and the anomaly areas are distributed within the influence range of anticlines. Simultaneously, soil and structural geochemistry show that F1, Nibao anticline, Erlongqiangbao anticline, and their transition areas all show good metallogenic elements (Au, As, and S) assemblage anomalies, with good metallogenic space and prospecting possibilities. There are five main hypotheses about the source of ore-forming fluids and Au in the Nibao gold deposit: (1) related to the Emeishan mantle plume activity; (2) source from the Emeishan basalt; (3) metamorphic fluid mineralization; (4) basin fluid mineralization; (5) related to deep concealed magmatic rocks; of these, the mainstream understanding is the fifth speculation. It is acknowledged that the ore-forming fluids are hydrothermal fluids with medium–low temperature, high pressure, medium–low salinity, low density, low oxygen fugacity, weak acidity, weak reduction, and rich in CO2 and CH4. The fluid pressure is 2–96.54 MPa, corresponding to depths of 0.23–3.64 km. The dating results show that the metallogenic age is ~141 Ma, the extensional tectonic environment related to the westward subduction of the Pacific Plate. Based on the above explanation, the genetic model related to deep concealed magmatic rocks of the Nibao gold deposit is established, and favorable prospecting areas are outlined; this is of great significance for regional mineral exploration and studying the genesis of gold deposits. [ABSTRACT FROM AUTHOR]

Rare earth elements (REE) in marine minerals have been widely used as proxies for the redox status of depositional and/or diagenetic environments. Phosphate nodules, which are thought to grow within decimetres below the sediment–water interface and to be able to scavenge REE from the ambient pore water, are potential archives of subtle changes in REE compositions. Whether their REE signals represent specific redox conditions or they can be used to track the overlying water chemistry is worth exploring. Through in situ laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS), we investigate the REE compositions of a drill-core-preserved phosphate nodule from the lower Cambrian Niutitang Formation in the Daotuo area, northeastern Guizhou Province, South China. REE distributions of the nodule show concentric layers with systematic decreases in Ce anomalies (Ce/Ce*) from the core to the rim. The lowest Ce/Ce* appears in the outer rim where REE concentrations are relatively high. These results are interpreted to reflect REE exchange with pore water at a very early stage or bathymetric variation during apatite precipitation. The origin of the shale-normalized middle REE (MREE) enrichment in our sample is less constrained. Possible driving factors include preferential MREE substitution for Ca in the apatite lattice, degradation of organic matter and deposition beneath a ferruginous zone. Although speculative, the last possibility is consistent with the chemically stratified model for early Cambrian oceans, in which dynamic fluctuations of the chemocline provided an ideal depositional context for phosphogenesis. [ABSTRACT FROM AUTHOR]

Lamproites and kimberlites are natural probes of the subcontinental lithospheric mantle providing insights into the Earth's continental lithosphere. Whole-rock major-, trace-element and Sr–Nd–Pb isotopic compositions of the Paleozoic (~ 253 Ma) lamproite dikes from the Baifen zone of the Zhenyuan area in southeastern Guizhou Province (in the southern Yangtze Block, South China) are presented. The Baifen lamproites are characterized by high MgO (7.84–14.1 wt%), K2O (3.94–5.07 wt%) and TiO2 (2.69–3.23 wt%) contents, low SiO2 (41.3–45.7 wt%), Na2O (0.21–0.28 wt%) and Al2O3 (6.10–7.20 wt%) contents. All lamproites have elevated Cr (452–599 ppm) and Ni (485–549 ppm) abundances, as well as high Ba (1884–3589 ppm), La (160–186 ppm), Sr (898–1152 ppm) and Zr (532–632 ppm) concentrations. They show uniform REE distribution patterns that are strongly enriched in light REEs relative to heavy REEs [(La/Yb)N = 71.1–87.6], and exhibit OIB-like geochemical features with obvious enrichment of both LILEs and HFSEs in the primitive mantle-normalized multi-element distribution diagram. Moderately radiogenic Sr (87Sr/86Sri = 0.706336–0.707439), unradiogenic Nd (143Nd/144Ndi = 0.511687–0.511704 and εNd(t) = − 12.2 to − 11.9), and low initial Pb (206Pb/204Pbi = 16.80–16.90, 207Pb/204Pbi = 15.34–15.35 and 208Pb/204Pbi = 37.43–37.70) isotopic compositions are obtained from the rocks. They yield old model ages of TDM(Nd) = 1.48–1.54 Ga. These signatures suggest that the Baifen lamproite magmas are alkaline, ultrapotassic and ultramafic in character and mainly represent mantle-derived primary melts, which have undergone insignificant crustal contamination and negligible fractional crystallization. The Baifen lamproites originated from a veined metasomatized lithospheric mantle source. We envisage that they were derived by partial melting of old, mineralogically complex metasomatic vein assemblages in the subcontinental lithospheric mantle beneath the southern Yangtze Block. The source region experienced ancient mantle metasomatism with complex modification by enriched fluids and melts. The metasomatic agents are most likely to originate from pre-existing slab subduction beneath the southeastern margin of the Yangtze Block. Tectonically, the Baifen lamproites were emplaced at the southern margin of the Yangtze Block, and they formed in an intraplate extensional setting, showing an anorogenic affinity. In terms of time and space, the genesis of Baifen lamproites is presumably related to the Emeishan large igneous province. The Emeishan mantle plume is suggested as an effective mechanism for rapid extension and thinning of the lithosphere, followed by decompression melting of the subcontinental lithospheric mantle. Combined with the thermal perturbation from asthenospheric upwelling induced by the Emeishan mantle plume, the lamproite magmas, representing small volume and limited partial melts of ancient enriched mantle lithosphere, arose. We propose that the generation of the Baifen lamproite dikes probably was a consequence of the far-field effects of the Emeishan mantle plume. [ABSTRACT FROM AUTHOR]

The fault-controlled Nibao Carlin-type gold deposit, together with the strata-bound Shuiyindong deposit, comprise a significant amount of the disseminated gold deposits in southwestern Guizhou Province, China. Five main types and two sub-types of pyrite at the Nibao deposit (Py1a/Py1b, Py2, Py3, Py4, Py5) were distinguished based on detailed mineralogical work. Py1, Py2 and Py3 are Au-poor, whereas Py4 and Py5 are Au-rich, corresponding to a sedimentary and hydrothermal origin, respectively. Through systematic in situ analyses of NanoSIMS sulfur isotopes, the framboid pyrite Py1a with negative δ34S values (− 53.3 to − 14.9‰) from the Nibao deposit were found to originate from bacterial sulfate reduction (BSR) processes in an open and sulfate-sufficient condition while the superheavy pyrite Py1b (73.7–114.8‰) is probably due to the potential influence of closed-system Rayleigh fractionation or the lack of preservation of deep-sea sediments. Data of Py2 and Py3 plot within the area of S isotope compositions from biogenic and abiogenic sulfate reduction. In view of few coeval magmatic rocks in the mining district, the near zero δ34S values of the Au-rich pyrites (Py4 and Py5) may discount the potential involvement of magmatic but metamorphic or sedimentary origin. LA-ICP-MS and TEM work show that Au in ore-related pyrite is present as both nanoparticles and structurally bound. LA-ICP-MS analyses show that the Au-rich pyrite also contains higher As, Cu, Sb, Tl and S than other types of pyrite, which inferred a distal manifestation of deep hydrothermal mineralization systems. [ABSTRACT FROM AUTHOR]

The black shale series that formed in the Ediacaran-Cambrian transition are important stratigraphic records of the co-evolution of the paleo-ocean, -climate, and -biology. In this study, we measured Re-Os isotopic compositions of the black shale in the Niutitang Formation from the Gezhongwu section in Zhijin, Guizhou Province. The samples had high Re and Os contents, with Re ranging from 21.27 to 312.78 ng/g and Os ranging from 0.455 to 7.789 ng/g. The Re-Os isotope isochron age of 522.9 ± 8.6 Ma implies deposition of the Niutitang black shale predated the Chengjiang Fauna, providing an age constraint for the expansion of oceanic anoxia in the study area. The initial 187Os/188Os ratio of 0.826 ± 0.026 indicates that enhanced continental weathering might have triggered the expansion of the oceanic anoxia. [ABSTRACT FROM AUTHOR]

The Paiting gold deposit, Guizhou Province, China, has been regarded as a Carlin-type gold deposit by several researchers. Alteration and ore-related minerals from the Paiting deposit were examined, and results were compared with the Cortez Hills Carlin-type gold deposit, Nevada, USA. Similarities include the structural and stratigraphic controls on the orebodies in both deposits and the occurrence of invisible gold ionically bound in arsenian pyrite. Significant differences include the following: (1) The gold-bearing mineral in Nevada is arsenian pyrite. However, gold-bearing minerals in the Paiting deposit include arsenopyrite, arsenian pyrite, and trace pyrrhotite. Also, euhedral or subhedral gold-bearing arsenian pyrite at Paiting contains significantly less As, Cu, and Hg than gold-bearing pyrite from Nevada. (2) Alteration in the Paiting deposit displays significantly less decarbonatization. Instead, dolomite precipitation, which has not been described in Nevada deposits, is associated with deposition of gold-bearing sulfide minerals. (3) Stibnite and minor native antimony typify Paiting late-ore-stage minerals, whereas in Nevada, realgar, orpiment, and calcite are common late-ore-stage minerals. Precipitation of native antimony in the Paiting deposit reflects the evolution of a late-ore fluid with unusually low sulfur and oxygen fugacities. Some characteristics of the Paiting gold deposit, including formation of ore-stage dolomite and precipitation from CO-rich ore fluids at temperatures in excess of 250 °C, are more typical of orogenic deposits than Nevada Carlin deposits. The presence of similarities in the Paiting deposit to both Carlin type and orogenic deposits is consistent with formation conditions intermediate to those typical of Carlin type and orogenic systems. [ABSTRACT FROM AUTHOR]

Arsenian pyrite in the Shuiyindong Carlin-type gold deposit in Guizhou, China, is the major host for gold with 300 to 4,000 ppm Au and 0.65 to 14.1 wt.% As. Electron miroprobe data show a negative correlation of As and S in arsenian pyrite, which is consistent with the substitution of As for S in the pyrite structure. The relatively homogeneous distribution of gold in arsenian pyrite and a positive correlation of As and Au, with Au/As ratios below the solubility limit of gold in arsenian pyrite, suggest that invisible gold is likely present as Au in a structurally bound Au complex in arsenian pyrite. Geochemical modeling using the laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of fluid inclusions for the major ore forming stage shows that the dominant Au species were Au(HS) (77%) and AuHS (23%). Gold-hydroxyl and Gold-chloride complexes were negligible. The ore fluid was undersaturated with respect to native Au, with a saturation index of −3.8. The predominant As species was HAsO. Pyrite in the Shuiyindong deposit shows chemical zonation with rims richer in As and Au than cores, reflecting the chemical evolution of the ore-bearing fluids. The early ore fluids had relatively high activities of As and Au, to deposit unzoned and zoned arsenian pyrite that host most gold in the deposit. The ore fluids then became depleted in Au and As and formed As-poor pyrite overgrowth rims on gold-bearing arsenian pyrite. Arsenopyrite overgrowth aggregates on arsenian pyrite indicate a late fluid with relatively high activity of As. The lack of evidence of boiling and the low iron content of fluid inclusions in quartz, suggest that iron in arsenian pyrite was most likely derived from dissolution of ferroan minerals in the host rocks, with sulfidation of the dissolved iron by HS-rich ore fluids being the most important mechanism of gold deposition in the Shuiyindong Carlin-type deposit. [ABSTRACT FROM AUTHOR]