Characteristics of the ore-forming fluid in the Huayuan Pb-Zn ore filed, Northwest of Hunan Province, China

1 Geological Setting The Huayuan Pb-Zn ore field in Xiangxi is located in the southeastern margin of the Yangtze block and the mid-segment of the West Hunan-West Hubei metallogenic belt.The exposed stratum are the lower

Geology,Geochemistry,and Genesis of the Tongcun Reduced Porphyry Mo(Cu) Deposit,NW Zhejiang Province,China

The Tongcun Mo（Cu） deposit in Kaihua city of Zhejiang Province,eastern China,occurs in and adjacent to the Songjiazhuang granodiorite porphyry and is a medium-sized and important porphyry type ore deposit.Two irregular Mo（Cu） orebodies consist of various types of hydrothermal veinlets.Intensive hydrothermal alteration contains skarnization,chloritization,carbonatization,silicification and sericitization.Based on mineral assemblages and crosscutting relationships,the oreforming processes are divided into five stages,i.e.,the early stage of garnet ＋ epidote ± chlorite associated with skarnization and K-feldspar ＋ quartz ± molybdenite veins associated with potassicsilicic alteration,the quartz-sulfides stage of quartz ＋ molybdenite ± chalcopyrite ± pyrite veins,the carbonatization stage of calcite veinlets or stockworks,the sericite ＋ chalcopyrite ± pyrite stage,and the late calcite ＋ quartz stage.Only the quartz-bearing samples in the early stage and in the quartzsulfides stage are suitable for fluid inclusions（FIs） study.Four types of FIs were observed,including1） CO2-CH4 single phase FIs,2） CO2-bearing two- or three-phase FIs,3） Aqueous two-phase FIs,and4） Aqueous single phase FIs.FIs of the early stages are predominantly CO2- and CH4-rich FIs of the CO2-CH4-H2O-NaCl system,whereas minerals in the quartz-sulfides stage contain CO2-rich FIs of the CO2-H2O-NaCl system and liquid-rich FIs of the H2O-NaCl system.For the CO2-CH4 single phase FIs of the early mineralization stage,the homogenization temperatures of the CO2 phase range from 15.4 ℃ to 25.3 ℃（to liquid）,and the fluid density varies from 0.7 g/cm^3 to 0.8 g/cm^3;for two- or three-phase FIs of the CO2-CH4-H2O-NaCl system,the homogenization temperatures,salinities and densities range from 312℃ to 412℃,7.7 wt%NaCl eqv.to 10.9 wt%NaCl eqv.,and 0.9 g/cm^3 to 1.0 g/cm^3,respectively.For CO2-H2O-NaCI two- or threephase FIs of the quartz-sulfides stage,the homogenization temperatures and salinities range from255℃ to 418℃,4.8 wt%NaCl eqv.to 12.4 wt%NaCl eqv.,respectively;for H2O-NaCl two-phase FIs,the homogenization temperatures range from 230 ℃ to 368 ℃,salinities from 11.7 wt%NaCl eqv.to16.9 wt%NaCl eqv.,and densities from 0.7 g/cm^3 to 1.0 g/cm^3.Microthermometric measurements and Laser Raman spectroscopy analyses indicate that CO2 and CH4 contents and reducibility（indicated by the presence of CH4） of the fluid inclusions trapped in quartz-sulfides stage minerals are lower than those in the early stage.Twelve molybdenite separates yield a Re-Os isochron age of 163 ± 2.4 Ma,which is consistent with the emplacement age of the Tongcun,Songjiazhuang,Dayutang and Huangbaikeng granodiorite porphyries.The 〈S18OSMow values of fluids calculated from quartz of the quartz-sulfides stage range from 5.6‰ to 8.6‰,and the 〈JDSMOw values of fluid inclusions in quartz of this stage range from-71.8‰ to-88.9‰,indicating a primary magmatic fluid source.〈534SV-cdt values of sulfides range from＋1.6‰ to ＋3.8‰,which indicate that the sulfur in the ores was sourced from magmatic origins.Phase separation is inferred to have occurred from the early stage to the quartz-sulfides stage and resulted in ore mineral precipitation.The characteristics of alteration and mineralization,fluid inclusion,sulfur and hydrogen-oxygen isotope data,and molybdenite Re-Os ages all suggest that the Tongcun Mo（Cu） deposit is likely to be a reduced porphyry Mo（Cu） deposit associated with the granodiorite porphyry in the Tongcun area.

Spatial and Temporal Distribution of Au and Pb-Zn Mineralization:Phenomenon,Mechanism and Implication

In the 1990s, some median-large gold deposits have been discovered in several lead-zinc metallogenetic belts (e.g. the Qinling lead-zinc metallogenetic belt, Shanxi Province and Gansu Province and the Qingchengzi lead-zinc ore field, Liaoning Province) in China. Gold deposits and lead-zinc deposits spatially co-exist in the same tectonic setting; lead-zinc orebodies are commonly located below gold ore bodies. The host rocks of lead-zinc ore-bodies are conformably overlain by those of gold ore bodies. The age of gold mineralization is obviously younger than that of lead-zinc mineralization. Preliminary geochemical research has demonstrated the following: lead-zinc mineralization took place in a marine sedimentary-exhalative system, which had the characteristics of a high fluid/rock ratio, a high salinity and a high halide activity; meanwhile, most of gold was transported into the low-temperature hydrothermal plume and primarily enriched in sediments. During later (magmatism-) metamorphism- tectonism, gold was remobilized and transported into the metamorphic fluid which had the characteristics of medium- high temperatures, a low fluid/rock ratio and a low activity of halide, and precipitated at a favourable structural site. Therefore, the co-existence of gold and lead-zinc deposits and the separation of gold from lead-zinc result from the differences of chemical composition and circulation of ore fluids in the same tectonic unit. This phenomenon can be used as an important criterion in exploration.

A Preliminary Study on the Aghbolaq(Fe,Cu)Skarn Deposit,Oshnavieh,NW Iran:Constraints on Metasomatic Fluid Evolution

The Aghbolaq skarn deposit is located in the Urumieh-Golpayegan plutonic belt,NW Iran.The garnetite skarn(stageⅠ)has been intensely cross-cut by the magnetite-garnet skarn(stageⅡ)which were,in turn,cut and offset by the ore-hosting quartz veins/veinlets(stageⅢ).The predominance of andradite(Adr82.5–89.1)and its high Fe3+/Al ratio(up to 1685)apparently supports the high fO2,salinity and prevalence of magmatic/hydrothermal fluids involved,rather than meteoric waters,during the magnetite-garnet skarn formation.Two major groups of fluid inclusions,namely aqueous(LV,LVS)and aqueous–carbonic(LVC,LLCVC),were recognized in garnet and quartz veins that,especially in growth zones and along intra-granular trails,better display fluid inclusion assemblages(FIAs)than those in clusters.The prograde magnetite-garnet skarn was formed by the metasomatic fluid at relatively high Th(209–374℃),under a lithostatic pressure of~200 bars.The retrograde mineralized quartz veins were formed at temperatures ranging from 124℃to 256℃,by dilute and less saline(2.57–11.93 wt%NaCl eq.)hydrothermal fluids under a hydrostatic pressure of~80 bars.The fluid evolution of the Aghbolaq skarn began with an earlier simple cooling of metasomatic fluid during the prograde stage,followed by the later influx of low salinity meteoric fluids during the retrograde stage.

Mineral Components, Texture, and Forming Conditions of Hydrothermal Chimney on the East Pacific Rise at 9°-10°N

To characterize the hydrothermal processes of East Pacific rise at 9°-10°N, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope,scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely：（i） anhydrite ＋ marcasite ＋ pyrite, （ii） pyrite ＋ sphalerite ＋ chalcopyrite, and （iii） chalcopyrite ＋ bornite ＋ digenite ＋ covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall.

A metallogenic model for the supergiant gold system in Jiaodong province:Constraints from crustal velocity structure

We investigate the role of crustal architectures playing in controlling the genesis and nature of supergiant Jiaodong orogenic gold system via seismic imaging.We deployed an NWW-SEE-trending broadband seismic linear array traversing the province to construct a shear wave velocity(V_S)transect based on ambient noise tomography.Our crustal V_S transect reveals a prominent low velocity zone(LVZ)at 12–20 km depths across the whole province and high V_S anomalies at 8–12 km depths underneath the western part that hosts most of the ore tonnage.We interpret the former as a hydrothermal alteration zone related to mineralization and the latter as a crustal component containing large amounts of mafic rocks(e.g.,amphibolites).In addition,a listric fault system and a strike-slip fault system are imaged in the western and eastern parts of the province,respectively.Combining features of crustal velocities with regional geological observations that ores are tempo-spatially associated with mafic dikes,we propose a model of gold metallogenic processes.In this model,ponding and degassing of the mafic magmas led to the formation of a hydrothermal alteration LVZ in the middle crust prior to mineralization.Later,auriferous fluid was released from this intra-crustal hydrothermal alteration zone as it was heated by upwelling asthenosphere.The ore fluid ascending along the listric fault system possibly leached extra gold from the upper-crustal amphibolites.Then,the gold-rich fluid migrated up along different fault systems,leading to the disseminated-veinlet mineralization with great gold endowment in the western listric fault system and the quartz-vein type mineralization with relatively small ore tonnage in the eastern strike-slip fault system.