Rare Earth Element Geochemistry on Magmatic Rocks and Gold Deposits in Shizishan Ore-Field of Tongling, China

REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and Ce anomalous values, and ∑REE, ∑LREE/∑HREE regular changes, which indicates that their magmas come from the same source and their digenetic mechanism is fractional crystallization. In three gold deposits, the mineral ores and related altered rocks have similar chondrite-normalized REE patterns and sharp Eu positive anomalous values. The REE contents reduced from the magmatic rocks to skamization or alteration magmatic rocks, skam type ores, sulphide type ores, wall-rocks limestone or marble. The REE geochemical characteristics of the ores and related rocks show that primary fluids originated from magmatic differentiation in lower pressure of shallow crust, ore-forming hydrothermal solutions gained REE and mineralization elements further from leaching the magmatic rocks, then superimposed and reformed the limestones or marbles and deposited ore-forming material.

Metallogeny of the Lannigou Sedimentary Rock-hosted Disseminated Gold Deposit in Southwestern Guizhou Province,China

The Lannigou deposit is a large-sized sedimentary rock-hosted disseminated gold （SRHDG） deposit located in the Youjiang Basin. It is hosted by the Middle Triassic turbidite. Wall rock alterations, including silicification, pyritization, arsenopyritization, carbonatization and argillization, commonly occur along fractures. PGE study demonstrates that either Permian basalts or Triassic ultrabasic intrnsives are unlikely to be the main source of gold mineralization. Coupled with the lack of other nmgmatic activity in the vicinity of the mining area, an amagmatic origin is proposed. Organic matter compositions and GC-MS analysis of the ores and host rocks show that the organics in the ores and the host rocks have a common source; the organic matter in the ores was mainly indigenous. The positive correlation between S2 and Au contents, along with the common occurrence of organic inclusions, suggest involvement of organic matter in the ore-forming process in terms of promoting Au leaching from the source rocks, making colloidal Au migration possible, as well as hydrocarbon reduction of sulphate. Geological and geochemical characteristics of the Lannigou deposit suggest that it was formed through circulation of meteoric water and probably less importantly organic bearing formation water driven by high geothermal gradient caused by late Yanshanian extension, which leached Au from the source bed, and then migrated as Au-bisnlfides and colloidal Au, culminating in deposition by reduction-adsorption and surface complexation of gold onto the growth surface of arsenlan pyrite.

Metamorphic Rock-hosted Disseminated Gold Deposits——A Case Study of the Xiaotongjiapuzi Gold Depositof Eastern Liaoning

The Xiaotongjiapuzi gold deposit occurs in a Palaeoproterozoic rift accretionary terrane in eastern Liaoning and is hosted by a carbonate formation of the Dashiqiao Formation, Liaohe Group. The metamorphic grade of the host rock is low amphibolite-high greenschist facies. Gold, which is mainly invisible, is distributed in pyrite and arsenopyrite. The grains of Au-bearing sulphide minerals are fine, ranging from 0.0 n to 1 mm. The wall-rock alterations are characterized by low-temperature silification, hydro-sericitization, sericitization and carbonatization. The homogenization temperatures of the fluid inclusions in quartz closely associated with gold mineralization range from 140 to 240°C. The metallogenic age represented by the Ar-Ar isotopic age of sericite is 167 Ma. Comparisons and studies show that the Xiaotongjiapuzi gold deposit can be classified as the submicron-sized disseminated deposit (analogous to the Carlin-type) hosted in metamorphic rocks.

Fluid inclusion, siliceous rock geochemistry of Shewushan lateritic gold deposit, Hubei Province, eastern China: Implication for the genesis of primary orebody

The Shewushan gold deposit is located 16 km southwest of Jiayu County, Hubei Province, eastern China, which is the largest lateritic gold deposit in Asia, consisting of a series of mineralized faults containing gold grades of 1.0–19.5 g/t set within a larger, lower-grade(0.2–1.0 g/t) zone. According to the fluid inclusions study, the homogenization temperature ranges from 70–350℃, and concentrates between 140–220℃. The laser Rama results show that the CO2 and CH4 exist in mineralized fluid. In addition, the major and trace element and REE geochemical data show that the genesis of the siliceous rocks is hydrothermal genesis, formed by mineralized fluid bearing SiO2 transmitted along faults to the surface, and replace the carbonate rocks to begin deposition. Primary gold mineralization is attributed to hydrothermal activity that followed the main period of tectonic deformation of the Indosinian orogeny, which caused the regional detachment regime in southeast Hubei. The reversed fold and the fault system formed the fluid migration channel in the Shewushan area. EPMA results show that Au exists in arsenopyrite(850×10-6–1550×10-6 Au) and pyrite(470×10-6–1340×10-6 Au). Therefore, based on the above results and combined with the field observation, we suggest that the genesis of primary orebody in Shewushan deposit is carlin type, while not weathered residual type.

Characteristics of Element Migration in the Process of Wall-Rock Alteration in the Shibangou Gold Deposit,Western Henan

Abstract The Shibangou gold deposit in western Henan is associated with irregular quartz veinlets occurring in altered shear zones dissecting a dioritic intrusion. The altered shear zones are characterized by silicification, pyritization, sericilization, chloritization and K-feldspar alteration. Zoning of altered rocks adjacent to the Au-bearing quartz veins is obviously exhibited. Fine-grained sulphides and quartz veinlets of different ages and small-scale fissures are widely distributed in the central part of the altered zones. Major mineralization types in this gold deposit are Au-bearing quartz veinlets and altered rocks in the shear zones. Samples were collected from drilling cores according to the alteration zoning and mineralization type and all samples were analyzed for major and trace elements. Mass balance, volume change (fv=97.3–71.9%) and major element variation sequences are studied in terms of major elements. The changes of mobile components (SiO2, K2O, Fe2O3) and CaO) and immobile component (Al2O3) in the wall-rock alteration are discussed. The gold mineralization is associated with the enrichment of As, Ag, Hg and Pb and depletion of Cu and Zn. The study of compositional variation of altered rocks proves to be a very efficient method for defining the extent of wall-rock alteration, fluid activity and mineralization and enrichment.

Geochemical Characteristics of the Jinjiazhuang Ultrabasic Rock-Type Gold Deposit in Chicheng County, Hebei Province

The Jinjiazhuang gold deposit occurs in the Zhangjiakou gold field, Northwest Hebei. The ore bodies are mostly hosted in Xiaozhangjiakou ultrabasic rocks dominated by diopsidite. Electron microprobe analyses indicate that the deposit is characterized by the enrichment of some platinum group elements in principal metallic minerals such as chalcopyrite, galena, sphalerite and pyrite, and the presence of millerite. Stable isotope studies show that carbon, sulfur and most of the metallogenic elements were probably derived largely from the host Xiaozhangjiakou ultrabasic rocks and that it is possible that the ore\|forming fluid was predominated by meteoric water.

Geochemical Features of Ore Fluid for Gold Deposits Related to Alkaline Rocks in China

Fluid inclusion studies of 5 gold deposits connected with alkaline rocks show that quartz separated from auriferous quartz veins contains abundant three\|phase CO\-2\|NaCl\|H\-2O inclusions and two\|phase CO\-2\|dominated ones, measuring 5-20μm in diameter. Homogenization temperatures of the fluid inclusions are mostly within the range of 150-300℃, and the salinities, mainly 0.2wt%-12 wt%(NaCl). Gold mineralizations occurred at depths of 1.4-2.8 km. The most striking character of fluid composition is that among the cations, Na\++ is dominant, followed by K\++, Ca\+\{2+\}; among the anions, Cl\+- is slightly higher than SO\+\{2-\}\-4. In the evaporate, H\-2O is dominant, followed by CO\-2. The pH values are mainly within the range of 6.5-8.5,indicating that the ore\|forming solutions are alkaline in nature. The hydrogen and oxygen isotopic ratios indicate that the ore fluid is composed mainly of magmatic water. With the dropping of temperature in the ore fluid, the contents of CO\-2 decreased while the salinity increased. The relations between Au and other components of the ore fluid are discussed in the paper, and it is concluded that in these deposits, chlorides, H\-2S, SiO\-2,CO\-2 , etc. in the fluid all are involved in the migration and concentration of Au.

Simulation of rock mass balance of two typical altered rocks in Wulong gold deposit of Liaoning, China

Wulong gold deposit hosted in granite and fine-grained d io rite dikes, is a typical gold deposit of quartz vein type. Granite and fine-gra ined diorite dikes in the ore deposit were altered by metallogenic fluid. Based on the altered zoning, the samples of petrochemistry were collected and major an d trace elements were analyzed systematically. Calculation of rock mass balance shows that the major elements (SiO 2, K 2O, P 2O 5, Fe 2O 3) in the two ty pical altered rocks are clearly added into the altered system, and that trace el ements (V, Y, Zr, Ni, Co, Sr) assume an increasing and decreasing tendencies in the altered granite and altered diorite dike, respectively. The fluid/rock ratio s are 30.17-181.00 and 115.44-692.67 respectively for altered granite and alte red diorite dike, they have profoundly effects on metallogenesis.

CRUSTOBODY STRUCTURE OF CHINA AND DISTRIBUTION OF ROCK GOLD ORE DEPOSITS

CRUSTOBODY STRUCTURE OFCHINA AND DISTRIBUTION OFROCK GOLD ORE DEPOSITSHuang Ruihua(Changsha Institute of Geotectonics, Academia Sinica, 410013, Hunan, China)rock gold ore deposit, crustobody structure, China.China continent is divided into four crustobodies from east to west. There is well-known Jinguashi rock gold deposit in East Asia continental margin crustobody. Gold met-allization is very well developed in East Asia crustobody. There are mainly rock gold ore de-posits related to Archean greenstone formation and Mesozoic-Cenozoic rock gold ore deposits in it. There are mainly Palaeozoic rock gold ore deposits of geosynclinal type and Cenozoic rock gold ore deposits of diwa (depression) type in Central Asia crustobody. South Asia crustobody possesses great potential in rock gold metallization. As a whole, prospecting exploration and exploitation of rock gold are very well of future in China.

Geology and Geochemistry of Reworking Gold Deposits in Intrusive Rocks of China-I.Features of the Intrusive Rocks

Most gold deposits in intrusive rocks were formed as a result of reworking processes.The intrusive rocks containing gold deposits and consisting of ultramafic-mafic, intermediate-acid and alkaline rocks of the Archean, Proterozoic, Caledonian, Hercynian and Yenshanian periods occur in cratons, activated zones of cratons and fold belts. Among them, ultramafic-mafic rocks, diorite, alkaline rocks, and anorthosite are products of remelting in the mantle or mantle-crust or mantle with crustal contamination. However, auriferous intermediate-acid rocks are products of metasomatic-remelting in auriferous volcanic rocks or auriferous volcano-sedimentary rocks in the deep crust.

Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit, southeastern Tibet: Contrast with carlin gold deposit

Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1) replacement of earlier magnetite by pyrite and carbonaceous material;(2) alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate (mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits.

Undersea safety mining of the large gold deposit in Xinli District of Sanshandao Gold Mine

The exploration of undersea resources becomes popular as land resources decrease. Researches were conducted with emphasis on the safety and efficiency of undersea mining of the large gold deposit in Xinli District of Sanshandao Gold Mine. A series of tests for the physical and mechanical characteristics of rock mass were carried out, and the three-dimensional geo-stress distribution was tested in the mining area. Further, a similar experimental simulation platform, which revealed the mechanism of water inrush and ascertained the reason- able thickness of the safety isolate layer, was established for the undersea mining. Meanwhile, the feasibility of cancelling the ore pillars and the safety conditions was checked by numerical simulation. The simulation results show that it is safe to exploit the ore body below the -85 m level （presently, the exploitation level is below -160 m in Xinli District）, and the ore pillars can be cancelled below the -560 m level. Fur- thermore, a novel backfill method was designed to reduce the rock strata disturbance and settlement, and the settlement of roof strata was monitored during the mining process. Engineering practice shows that the settlement of roof strata was small and that no disaster happened. This indicates that the undersea safety mining technology of the large gold deposit is achieved in Xinli District.

GEOCHEMICAL KINETIC SIMULATION ON WALL-ROCK ALTERATION ZONING IN THE BAOBAN GOLD FIELD, SOUTH CHINA

The Baoban gold field, located in the area of Hainan Island, South China, bears three gold de-posits: Tuwaishan, Baoban, and Erjia, which belong to the wall-rock alteration type. In terms of the petrography data, four alteration zones can be recognized from the ore-vein outwards: (1) the silicification zone; (2) the sericitization zone, (3) the chloritization zone; and (4) the calcitization zone. The geochemical kinetic simulation was carried out on sericitization and chloritization . Results of the study showed that the formation of the alteration zones is connected with the properties of hydrothermal fluids: the initial concentration of Al (O H)3, the diffusion coefficient and the velocity of fluid flow. The alteration zones in this field are the result of multiple interaction between hydrothermal fluids and wall rocks.

Metallogeny of Shoshonite-Hosted Copper-Gold Deposits in Middle-South Parts of Tancheng-Lujiang Deep Fault Zone and Its Vicinity, Eastern China

The middle south parts of Tancheng Lujiang deep fault zone and its vicinity are an important locality of Cu Au deposits related to Mesozoic volcanic subvolcanic magmatism in eastern China. According to their metallogenic features and ore forming conditions, copper gold deposits in this district are ascribed to two groups: the epithermal group which can be further divided into tellurium gold type, quartz adularia type and quartz manganoansiderite type; the magmatic hydrothermal group which includes porphyry Cu Au deposit, breccia pipe porphyry type Au Cu deposit and skarn type Au Cu deposit. In this paper, characteristics of six typical shoshonite hosted Cu Au deposits are outlined. Additionally, the factors that control the metallogenesis and distribution of these Cu Au deposits are discussed preliminarily.

The Structure of Ore-controlling Strain and Stress Fields in the Shangzhuang Gold Deposit in Shandong Province,China

The Shangzhuang altered-rock type gold ore deposit is located in the middle segment of and controlled by the Wang＇ershan fault zone in the northwestern part of the Jiaodong gold province, China. The deformation evolution, the structure of strain and stress fields and its ore-controlling effect in the Shangzhuang deposit are discussed in this paper. It is revealed that the deformation evolution has mainly undergone four phases： the early ductile deformation, the second NE-striking horizontal simple shear, the third NE-striking compression-shear and the final NW-striking compression. The mineralization happened during the third stage in which the maximum principal stress gradually transited from NE to NW. The 3-D numerical simulations of the stress field show that, on the condition that the maximum principal stress is NE-striking, the fracture development in the fault zone is favored, while when the maximum principal stress is NW-striking, the fault zone is relatively extensional and it is suitable for the influx and emplacement of ore-forming fluids. The compression-shear strain field during the mineralization is characterized by the λ-type structure, the positive flower structure, etc. Orebodies are mostly equidistantly located in the dilatational spaces, which are distributed in the integral compressional circumstances. And the dilatational spaces are developed where the fault attitude changes or shear joint systems develop. In the overall compression-shear stress field, the strain field bears self-similarity at multiple scales, including the orebody, ore deposit and orefield. The selfsimilarity of the structure comprises the subequidistant distribution of fractures at the same scale and the similar shape of the fractures at various scales. Yet, due to the special geological structure, the orebodies are mostly located in the hanging wall in the Shangzhuang deposit, which is different from most deposits in the Jiaodong gold province. Analyses of the ore-controlling stress and strain fields in the deposit provide an important basis for deposit seeking.

Geology, Geochemistry and Genesis of the Mazhuangshan Gold Deposit in Hami, East Tianshan, Xinjiang, China

The Mazhuangshan area is located in the east of the Aqikekuduke Island Arc, where there are distributed intermediate\|acid magmatic rocks emplaced during the Middle\|Late Carboniferous. There are more than 20 orebodies in the area with an average gold grade \{6.4\}×10\+\{-6\} at present. The dominant metallic minerals are natural gold, auriferous silver, natural silver, pyrite and galena. Pyrite is the key gold carrier, high in Fe and low in S. Wall\|rock alterations mainly include pyritization, silicification, and sericitization. Carbonation alteration was extensive at the late stage, often resulting in a high\|grade orebody. Three mineralization stages may be distinguished. \; The peak homogenization temperatures of primary fluid inclusions range from 240 to 260℃. Mineralization pressures and depths are 47.2-68.8 MPa and 1.6-2.3 km respectively, showing the ore\|forming features of hypergene gold deposit. The average salinity is 15 wt% NaCl equivalent. Fluid inclusion geochemistry data show that Ca\+\{2+\} is far higher than Mg\+\{2+\}, and m\-\{K\++\}/m\-\{Na\++\}, m\+2\-\{Na\++\}/m\-\{Ca\+\{2+\}\} (\{0.001\}～\{0.338\}), m\-\{∑Cl\}/m\-\{∑S\} and m\-\{∑C\}/m\-\{∑S\} ratios change with the reduction parameter \R=(CO+CH\-4)/CO\-2\] and temperature. And the gold contents of ores and gangues are positively correlated with and temperature. And the gold contents of ores and gangues are positively correlated with R. \; The pH values of inclusion water in quartz range from 5.8 to 7.4. Oxygen fugacity (f\-\{O\-2\}) ranges from 10-55 Pa to 10-47 Pa, sulfur fugacity (f\-\{S\-2\}) is about 10-13, and Eh values are estimated to be about -0.6 eV. The \{δ\{\}\+\{34\}S\} values of the fluid were determined to be \{+3.94‰\} to \{+4.98‰\}. \{\{\}\+\{206\}Pb\}/\{\{\}\+\{204\}Pb\} and \{\{\}\+\{207\}Pb\}/\{\{\}\+\{208\}Pb\} ratios in pyrite are \{18.269\}-\{18.352\}, \{15.550\}-\{15.633\} and \{38.077\}-\{38.355\}, respectively. The ΣREE values (\{4.7\}×10\+\{-6\}～\{43.1\}×10\+\{-6\}) of ores and gangues are obviously lower than those of the host magmatic rocks, but their REE and trace element spider diagrams are similar to those of the host magmatic rocks, suggesting that the water consists dominantly of meteoric water, mixed with a part of magmatic water. The metallogenic element mostly came from magmatites. The deposit is closely related to host magmatic rocks. The deposit is classified as a Middle\|Late Carboniferous hypabyssal meso\| and hypothermic gold deposit.

The Physico-Chemical Conditions for Mobilization of Gold in Mobin Gold Deposit,Southwest Hunan, China

Experiments on water\|rock interaction were carried out on wall\|rock samples from the Mobin gold deposit, Southwest Hunan, China, with the aim of determining the optimum physical and chemical conditions for the mobilization of gold in solution. Results indicate that gold is most easily mobilized from the wall rock\|tuffaceous slate of the Mobin Deposit. Mobilization is optimized if fluids are neutral to slightly alkaline and contain both chlorine and sulphur ions at the concentration and composition of about \[0.25M (NH\-4)\-2S+1M NaCl\]. The amount of gold leached from the tuffaceous slate increases with temperature although the effect decreases above about 200℃.

Important Geological Factors Controlling the Formation of Gold Deposits in East China

The major gold deposits in East China are characterized by their occurrence in pre-Cambrian host metamorphic rocks, restriction in some specific stratigraphic-structural terranes,tendentious localization in ductile or ductile-brittle shear zones, association with the syntexis-type granitoids, and significant remobilization, superimposition and enrichment by the later-stage Mesozoic tectono-magmatic activities.

Transport and Concentration of Gold in Metamorphic-hosted Reworked Gold Deposits,China

Calculations based on the available thermodynamic data of AuCl2^- and Au(HS)2^- indicate that AuCl2^- is responsible for the transport and enrichment of gold during the stage of pre-concentration in the source bed while Au(HS)2^- is the main gold species involved in the formation of gold deposits in response to hydrothermal reworking .Acid chloride solutions with αcl^->10° and sulfur-rich solutions with a∑s in excess of 10^-2 are held as important criteria for gold enrichment in the source bed and for the formation of gold deposits by subsequent hydrothermal event, respectively.

Ore-Search Perspective for Superlarge Gold Deposits in the Jiaolai Basin of the Jiaodong Gold Metallogenetic Domain

There are three types of gold deposits in the Jiaodong gold metallogenetic domain. The strata\|bound gold deposits are a new type, which occur in a hydrocarbon\|gold double\|source bed enriched in gold (Au 174 ng/g) and organic carbon (0.007%-4.225%). At diagenetic and hydrothermal stages water and oil were simultaneously activated and the strata\|bound gold deposits were formed from interactions between water, oil and rocks. In the late Yanshanian period, gold orebodies were enriched and enlarged in response to tectonomagmatism and action of complex ore\|forming hydrothermal solutions. As a result, it is highly expected to find suparlarge gold deposits and the Yanzi area is expected to be a perspective target area.