Melt extraction and mineralization: A case study from the Shuangjianzishan supergiant Ag-Pb-Zn deposit(208 Mt), Inner Mongolia, NE China

The supergiant Shuangjianzishan(SJZ) Ag-Pb-Zn deposit is in the southern segment of the Great Hinggan Range(SGHR), northeast China. Previous studies suggest the ore-forming material and fluid originated from the magmatic system, and the mineralization age was consistent with the diagenetic age. However,the relationship between granitic magmatism and mineralization is still unclear in the SJZ. In this study, CH-O-He-Ar and in-situ S-Pb isotope analyses were conducted to determine the sources of ore-forming fluids and metals, which were combined with geochemistry data of SJZ granitoids from previous studies to constrain the relationship between the magmatism and the mineralization. The C-H-O-He-Ar-S-Pb isotopic compositions suggested the SJZ ore-forming material and fluids were derived from a magmatic source, which has mixed a small amount of mantle-derived materials. In addition, the disseminated sulfide from the syenogranite has comparable S-Pb isotopic composition with the sulfide minerals from ore veins,suggesting that the generation of the SJZ ore-forming fluids has a close relationship with the syenogranite magmatism. Combining with the geochemical characters of the syenogranite, the authors proposed that the mantle-derived fingerprint of the SJZ ore-forming fluid might be caused by the parent magma of the syenogranite, which was derived from partial melting of the juvenile lower crust, and underwent the residual melts segregated from a crystal mush in the shallow magma reservoir. The extraction of the syenogranite parent magma further concentrated the fertilized fluids, which was crucial to mineralization of the SJZ Ag-Pb-Zn deposit.

Metallogenic model of the Shuangjianzishan Ag-Pb-Zn district,Northeast China:Revealed from integrated geophysical investigation

The Shuangjianzishan deposit in Inner Mongolia is a typical Ag-Pb-Zn deposit of the southern Great Xing’an Range.Proven reserves of Ag,Pb,and Zn in this deposit have reached the scale of super-large deposits,with favorable metallogenic conditions,strong prospecting signs,and high metallogenic potential.This paper reports a study involving integrated geophysical methods,including controlled-source audio-frequency magnetotelluric,gravity,magnetic,and shallow-seismic-reflection methods,to determine the spatial distribution of ore-controlling structures and subsurface intrusive rock for a depth range of<2000 m in the Shuangjianzishan ore district.The objective of this study is to construct a metallogenic model of the ore district and provide a scientific basis for the exploration of similar deposits in the deep and surrounding regions.We used three-dimensional inversion for controlled-source audio-frequency magnetotelluric data based on the limited memory quasi-Newton algorithm,and three-dimensional physical-property inversion for the gravity and magnetic data to obtain information about the subsurface distribution of ore-controlling structures and intrusive rocks.Under seismic reflection results,regional geology,petrophysical properties,and borehole information,the geophysical investigation shows that the Dashizhai group,which contains the main ore-bearing strata in the ore district,is distributed within a depth range of<1239 m,and is thick in the Xinglongshan ore block and the eastern part of the Shuangjianzishan ore block.The mineralization is spatially associated with a fault system characterized by NE-,NW-,and N-trending faults.The magnetic and electrical models identify large,deep bodies of intrusive rock that are inferred to have been involved in mineralization,with local shallow emplacement of some intrusions.Combining the subsurface spatial distributions of ore-bearing strata,ore-controlling faults,and intrusive rock,we propose two different metallogenic models for the Shuangjianzishan ore district,which provide a scientific basis for further prospecting in the deep regions of the ore district and surrounding areas.

冀北牛圈银金矿及营房银铅锌矿深部成矿预测

对冀北牛圈银金矿和营房银铅锌矿矿床特征和相互关系的研究认为,营房矿体西部的硅化体及硅化花岗岩质角砾岩系成矿前断裂F1形成的,由于成矿后断裂F2大幅度的右行推覆作用,使原处于同一水平上的银金矿,在营房矿区被掩埋在深部,而深部的银铅锌矿却被推移到了浅部目前的位置;牛圈银金矿深部的铅锌矿未受到后期F2断裂的波及,可能完整地被保留在深部原位。根据地质、地球化学研究,提出了"在牛圈矿体深部找营房矿体,到营房矿体深部找牛圈矿体"的深部找矿方向。

Factors Controlling Deposition of Metallic Minerals in the Meng’entaolegai Ag-Pb-Zn Deposit, Inner Mongolia, China: Evidence from Fluid Inclusions, Isotope Systematics, and Thermodynamic Model

The Meng’entaolegai Ag-Pb-Zn vein-type deposit in Inner Mongolia,NE China is hosted in biotite/muscovite granite.This deposit includes the western(Zn-rich,deepest),middle(Zn-Pb rich)and eastern(Pb-Ag-rich,shallowest)ore-blocks.To better understand the metallogenic processes in ore district,we have undertaken a series of studies including fluid inclusion microthermometry,H-O-S-Pb isotope compositions and thermodynamic modeling.Based on fluid inclusion petrography,microthermometry results and HO isotope compositions,the ore-forming H2O-NaCl fluid inclusions are characterized by medium temperature and medium salinity.And two kinds of fluid processes(boiling in western and middle ore-block and fluid mixing in the eastern ore-block)were identified to explain the ore fluid evolution.More importantly,log ?O2-pH diagrams of δ^34S contours with the stability fields of Fe-and Cu-,Zn-,Pb-,and Ag-bearing minerals were constructed to restore the physicochemical conditions of ore-forming fluid in the western(270℃ and 80 bars),middle(250℃ and 70 bars),and eastern(230℃ and 50 bars)ore-blocks.As a result,the ore-forming conditions in the western and middle ore-block were similar.In the eastern ore-block,the fluids may have changed from acidic,S-poor and δ^34S(ΣS)≈2.8 to neutral,S-richer and δ^34S(ΣS)≈0.5,which imply that neutral S-rich meteoric water was mixed with the magmatic fluid.Meanwhile,the activity of Ag+was estimated to be about 10 ppm–9 ppm in the middle ore-block,but in the eastern ore-block it was about^10 ppm–12 ppm.We proposed that the key for Ag ore deposition was likely to be neutralization led by fluid mixing.

Geology,Mineralogy,and Isotopic Characteristics of the Zhonghe Ag-Pb-Zn Deposit,Western Henan Province,Central China

Located in Luoning County,western Henan Province,Central China,the Zhonghe Ag-Pb-Zn ore field,is a newly discovered deposit in the Xiaoshan District.Ore bodies controlled by NNW Faults occur as veins within the Paleoproterozoic Xiong’er Group or the Early Cretaceous porphyritic granite.Given that the Zhonghe deposit has been covered by thick Quaternary sediments,the paragenetic mineral assemblage was determined mainly by microscopic observations,including the quartzsiderite-pyrite alteration (StageⅠ),polymetallic sulfide precipitation (StageⅡ),silver mineralization(Stage Ⅲ),and quartz-carbonate stage (StageⅣ).The host minerals for silver are diverse,such as freibergite,pyrargyrite,polybasite,argyrodite,canfieldite,argentite,and native silver,whereas those for Pb and Zn are galena and sphalerite,respectively.In order to constrain the ore-forming components of the Zhonghe deposit,a combined in-situ analysis was conducted on represented sulfides from StageⅡand Stage Ⅲ.In-situ δ^(34)S values of the analyzed sulfides,including the pyrite,chalcopyrite,sphalerite,and galena,display a relatively narrow range (0.90‰-5.0‰),which is close to magmatic sulfur source.The ^(206)Pb/^(204)Pb and^(207)Pb/^(204)Pb ratios show a narrow range (17.140-17.360 and 15.385-15.490),whereas the ^(208)Pb/^(204)Pb ratios exhibit a broad variation (36.601-37.943),indicating a contamination of the Xiong’er Group.Synthesis of geochronological and geochemical data from the Xiaoshan District,we contend that the ore-forming materials of the Zhonghe Ag-Pb-Zn deposit are originated from the lower crust,which has presumably been influenced by the large-scale lithospheric delamination of the eastern North China Craton during the Early Cretaceous.In consideration of the geological setting,mineralogy,and geochemical compositions,we suggest that the Zhonghe Ag-Pb-Zn deposit is characterized as intermediate sulfidation type epithermal deposit,and may be a potential exploration target for porphyry Mo-Cu deposits.

河北丰宁营房铅锌银矿床银的赋存状态及富集规律

河北丰宁营房铅锌银矿床产于一近南北向的中型韧性剪切带中。矿体定位于燕山早期粗粒钾长花岗岩与下元古界红旗营子群地层构造接触带中。矿体埋藏浅、厚度大、品位高，已构成铅锌银共生矿床。主要银矿物有银黝铜矿、辉银矿、螺状硫银矿、浓红银矿及自然银等。银主要以单矿物形式赋存于方铅矿及闪锌矿中，少量存在于脉石中，极少量以类质同像或次显微包体形式存在于硫化物和硫盐矿物中。银的富集主要与方铅矿、闪锌矿及黄铁矿关系密切，而单一黄铁矿型或黄铁多于方铅矿＋闪锌矿类型的矿石，银矿化一般不好。银矿化程度与糜棱岩化程度及硅化、绢云母化程度正相关。经初步研究，矿体的直接围岩（红旗营子群变质岩）为初始矿源层，而花岗岩的侵入，只起到了热动力源的作用。矿源层中的成矿物质在韧性剪切糜棱岩化过程中，在热动力变质作用下发生变质分异而活化、迁移、富集成矿。矿床成因类型应属变质（热液）分异或韧性剪切糜棱岩型铅锌银矿床。

Fluid-rock interactions leading to the formation of the epithermal Ag-Pb-Zn veins:A perspective of thermodynamic modeling

Although vein-type silver-lead-zinc ore deposits have been extensively studied,the factors controlling their formation are still poorly understood and their genesis is a matter of ongoing debate.In this contribution,I present new mineralogical data and the results of thermodynamic modeling that constrain the conditions of metal transport and deposition for the Aerhada epithermal Pb-Zn-Ag deposit(reserves of>1,000 t Ag@58 g/t and 1.0 Mt Pb+Zn@5.2%)in NE China.Three primary paragenetic stages have been identified,the second of which(Stage II)is the main base metal and silver mineralization.Freibergite,argentite,pyrargyrite,and canfieldite are the main Ag-bearing minerals and are spatially associated with an alteration assemblage of quartz-muscovite±chlorite±epidote.Dissolution textures and evidence of compositional heterogeneity for freibergite suggest that its decomposition may have redistributed the Ag and contributed in part to the high Ag grade ores in the deposit.Thermodynamic calculations indicate that there was extensive silver ore deposition from a strongly reducing(e.g.,∆log fO_(2)(HM)of<-8.6 to-2.4)and nearly neutral to weakly alkaline(e.g.,pH of 5.5 to 6.8)aqueous fluid at temperatures between 220℃ and 170℃.These calculations reveal that a reduction in fO_(2)and decreasing temperature,both as a result of fluid-rock interactions,were the key factors leading to silver and base metal mineral deposition.Further path modeling showed that the sole evolution of a magmatic-derived fluid is capable of forming the large Ag-Pb-Zn veins via fluid-rock interactions,which is contrary to the conclusions of some other studies that the mixture of an externally derived fluid is required to explain their formation.The genetic model for Ag-Pb-Zn ore formation developed in this study is applicable to other polymetallic vein-type deposits in comparable geological settings elsewhere.