Reworking Intensity—A Key Factor Leading to the Formation of Superlarge Gold Deposits in Greenstone Belts and Metamorphosed Microclastic Rocks in China

The greenstone belt and metamorphosed microclastic rock-type superlarge gold deposits in China are hosted in metamorphic rocks and later intrusive bodies.Sedimentation.regional metamorphism and mineralization contributed a lot to the formation of the deposits,so did remelting magmatic process to some deposits,but the deposits were finally formed by reworking processes.The key factor leading to the formation of superlarge gold deposits is the reworking intensity,which for superlarge gold deposits is reflected by the large-scale reworked source rocks and even ore materials of various sources,strongly oxidized ore-forming fluids with a long and repeated active history and stable geothermal heat current.The factor which decides the reworking intensity is the network consisting of structures of different classes.     

Geology, Geochemistry and Genesis of the Hongshijing Gold Deposit in Ruoqiang,Xinjiang

1IntroductionTheHongshijinggolddepositislocatedinthenorthofLuobupouLakeofRuoqiang ,about 30 0kmsouthwestofHamiCity ,Xinjiang .ItwasdiscoveredbytheSixthGeologicalTeamofXinjiangduringgeo chemicalexploration .TheHongshijinggolddeposit,whichoccursinthegold bearingformationcomposedofMiddleandLateCarboniferousvolcanicandpyroclasticrocks ,isabrittle ductileshearzonetypegolddepositcontrolledbyariftbelt.TheHongshijinggolddepositislocatedinthesouthwestoftheHongshi jing -Maotoushanmineralizationb…     

Genetic Analogy Between Sediment—Hosted Gold Deposits and Sediment—Hosted Copper Deposits in Southwest China

The sediment-hosted copper deposits according to the authors‘ study were formed from connate formation water during the post-sedimentary or diagenetic stage while the sediment-hosted disseminated gold deposits are unanimously considered to be of post-sedimentary hydrothermal origin.Therefore,apart from their own individulities.These two types of deposits must share some characters in common.Comparisons are attempted,in this paper,between the sediment-hosted copper deposits in southwest China and the Triassic sediment-hosted disseminated gold deposits in the Yunnan-Guizhou-Guangxi Triangle in terms of geological and geochemical features.     

A Three—Stage Metallogenic Model for Gold Deposits in Metamorphosed Microclastic Rocks

Gld deposits occurring in metamorphosed microcelastic rocks are distributed extensively at home and abroad.Some deposits of this type are of superlarge tonnage.The formation of gold deposits in metamorphosed microclastic rocks involves three stages:the sedimentary stage,the regionally metamorphic stage,and the ore-forming stage.At the first stage,microclastic sedimentary source rocks were developed in a relatively semi-enclosed reducing sea basin and were enriched in carbon,sulfur and gold.At the second stage,the gold adsorbed on organic matter and clay minerals was relesed and poorly concentrated during the destruction of organic matter and the depletion of clay minerals by regional metamorphism with increase temperature and pressure.At the third stage,a tectono-hydrothermal event took place.As a result,gold was leached from metamorphosed microclastic rocks,transported to ore depositional locus and/or mixed with gold of other sources in the course of migration,and finally precipitared as ores.Gold deposits of this type were eventually formed at the third stage,and they also can be classified as the orogenic belt type and the activation zone type.The gold deposits occurring in metamorphosed microcalastic rocks are the products of reworking processes and the influence of magmatism should be taken into consideration in some cases.     

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°C. 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 Ca²⁺ is far higher than Mg²⁺, and m_K ⁺/m_Na ⁺, m_Na^{2 +}/m_Ca ²⁺ (0.001∼0.338), m_ΣCl/m_ΣS and m_ΣC/m_ΣS ratios change with the reduction parameter [R = (CO + CH₄)/CO₂] and temperature. And the gold contents of ores and gangues are positively correlated withR.     

Quantitative Prediction of Concentrated Regions of Large and Superlarge Deposits in China

Identification and quantitative prediction of large and superlarge mineral deposits of solid mineral resources using the mineral resource prediction theory and method with comprehensive information is carried out nationwide in China at a scale of 1:5000000. Using deposit concentrated regions as the model units and concentrated mineralization anomaly regions as prediction units, the prediction is performed on GIS platform. The technical route and research method of locating large and superlarge mineral deposits and principle of compiling attribute table of independent variables and functional variables are proposed. Upon methodology study, the qualitative locating and quantitative predicting mineral deposits are carried out with quantitative theory Ⅲ and characteristic analysis, respectively, and the advatntage and disavantage of two methods are discussed. This research is significant for mineral resource prediction in ten provinces of western China.     

Deep－Source Ore－Forming Materials and Prospecting of Gold Deposits in Eastern Hebei,China

Eastern Hebei Province is one of the important gold mineralization areas in North China,and detailed investigations have been made in this area.Different mineralization models and different ore-formng surces have been proposed for the gold deposits in this area.As more detailed work was made and more information has been accumulated,it is necessary to make a new investigation on gold metallogenesis and its source.This paper presents the data about 13 gold deposits(occurrences.)It is concluded that the element gold came from the deep mantle.Different models of metallogenesis substantially describe such processes that ore-forming fluids were involved in metallogenesis in different favorable loci.Gold ore prospecting should be focused on fluid channel ways and favorable structures.     

Confirmation and Significance of Caledonian Metallogenic Epoch for Gold Deposits in South China

Caledonian gold deposits are widely distributed in South China.They are developed in both South China Caledonian fold belt and adjacent Proterozoic Jiangnan uplift.The host rocks are Proterozoic metamorphosed microclastic rocks in the Jiangnan uplift and Proterozoic and Cambrian strata,as well as Chengjiang and Caledonian igneous bodies in the South China flod belt.The distince differences between the Caledonian and the most developed Yenshanian glod deposits in South China are reflected in age and host-rock type,relations to Yenshanian magmatic activities,element association,mineral assemblage and glod deposit type.The studies have proven hat the Caledonian epoch is a principal metallogenic period of gold deposits in South China.This conclusion is of very important enlightening significance in exploration of Caledonian gold deposits in South China as well as in other Caledonian fold belts and adjacent uplifts in China.     

Silicon Isotope Geochemistry of Micro—Fine Disseminated Gold Deposits in SW Guizhou and NW Guangxi,China

Quartz was studied with respect to its silicon isotopic composition and cathodoluminescence in micro-fine disseminated gold deposits in SW Guizhou and NW Guangxi.The results showed that quartz in wall rocks.ores and that in association with hydrothermal silicification are distinctive in silicon isotopes and cathodoluminescence characters.Quartz in association with primary silicification is non-luminescent while that in wall rocks and associated with secondary silicification exhibits striking luminescence.Based on the dynamic fractionation of silicon isotopes,it is suggested that the mineralization was accompanied by rapid transport of aprimary siliceous fluid along the major deep fault system into subordinate faults before ore components deposited in favorable strata via penetration and metasomatism.Therefore,a deep origin is implicit for gold deposits of this type.     

Geological-Geochemical Characteristics of Carlin-and Carlin-Like-Type Gold Deposits in south Qinling Mountains

In this paper an intergrated geological and geochemical comparison is made of Carlintype and Carlin-like-type gold depostis in the region of South Qinling with their associated hydrothermal sedimentary lead-zinc pdposits,the Carlin-type deposits in the Yunnan-Guizhou-Guangxi gold triangle,China,the Carlin gold deposits,Carlin,western United States,and the Muruntau-type gold deposits in Uzbekistan.The comparative study indicates that the formation of these deposits has an intimate coupling relation with the mechanism of the tectonic movement of modern plates.Therefore,these deposits belong to those that were formed in the orogenic stage. They have the following similar characteristics:they are all sediment-hosted.occur in a tectonic environment of extensional rifting nature and show the characteristics of syngenetically modified mineralization.On the other hand,they alsso have noticeable differences:they are different in respect to their tectonic settings.association and structure of orogenic belts and complexity and strength of the modified mineralization.The regional tectonic evolution and extensive mineralization in orogenic belts are different expressions of the same continental dynamic process.     

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

Calculations based on the available thermodynamic data of AuCl ₂ ⁻ and Au (HS) ₂ ⁻ indicate that AuCl ₂ ⁻ 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 witha _Cl ⁻ > 10° and sulfur-rich solutions with a_Σs 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.     

Geology,Geochemistry and Genesis of Yinyan Porphyry Tin Deposit

The Yinyan porphyry tin deposit is a blind deposit associated with a small granite porphyry stock.The petrology and geochemistry of the Yinyan granite porphyry suggest that it is genetically of the transfor-mation type,emplaced at the late stage of fractional crystallization within a high-level magma chamber.Ore-forming fluids are derived predominantly from the granitic magma and they interact with the wall rocks intensely when finding their way upwards through the granite porphyry.From the lower part of the porphyry upwards the following alteration zones can be distinguished(a)slightly altered granite porphyry (with weak potash feldspathization),(b)protolithionite-quartz greisenization zone,(c)to-paz-quartz greisenization zone,(d)senicite-quartz sericitization zone,and （e）silicification zone (quartz core at the surface).Tin mineralization is related to greisenization,especially to topaz-quartz greisenization.Rock and ore-forming temperatures and oxygen fugacities are estimated,respectively.There are significant differences in many aspects between the Yinyan porphyry tin deposit and volcan-ic-subvolcanic porphyry tin deposits.     

The Discovery of Native Ruthenium in Nuanquanzi and Tuling—Shihu Gold Deposits：Implications for Source of Gold

Native ruthenium and platinum-bearing hedleyite were recognized two gold deposits contained in Archaean metamorphic rocks in northern China.They are coexistent with native gold,quartz and pyrite.The high W content of native ruthenium may reflect the precipitation of ores in a W-rich hydrothermal system at moderate to high temperatures,The presence of platinum-group minerals(PGM)in the two deposits suggests that Au and PGE were both derived from mantle-source rocks.     

Mode of Occurrence of Gold in Micro-Disseminated Strata-Bound Sb-Au Deposits,Qinling Region,China

Optical studies,backscattered electron images,secondary ion spectrometry and highprecision transmission electron imaging demonstrate that gold is strongly correlated with arsenic on a microscopic scale in the sediment-hosted micro-disseminated gold deposits.The positive correlation between Au and As,despite varying Au/As ratio,is persistent in arsenian pyrite overgrowths and arsenopyrite,It is found that gold occurs in native state as submicro beads in association with arsenic-bearing sulfides,The extremely small grain size of gold may indicate a very rapid process of deposition.     

吉林椅山金矿床成矿物质来源及成矿模式

椅山金矿成矿主要与燕山晚期牛心屯花岗岩有关，成矿时代为燕山晚期，成矿物质具有双重来源——地层与岩浆源。牛心屯花岗岩体内石英爆裂法系统测温资料表明，该岩体在岩浆结晶期后曾有一次普遍的中一高温热液作用——成矿热液源和成矿热源。侵入石缝组接触带的牛心屯花岗岩体的岩石化学研究表明，从岩体进入围岩的元素有Si，K，Na，Fe^3 等；围岩进入岩体的元素有Al，Mg，Ca，Fe^2 等。矿石硫同位素研究表明，重硫少、富轻硫，轻硫可能来自围岩。矿体中δ^18O研究证实矿体氧同位素大多数来自牛心屯花岗岩体，少量来自围岩。碳同位素组成特征反映金矿床内的碳来自围岩。     

Sediment—Hosted Gold Deposits in China_geochemistry and Prospecting

Sediment-hosted gold deposits are the major type of gold resources in china,Concen trated mostly in the two“Triangle Regios“,they are generally hosted in fine-clastic turbidite,hydrothermal chet and marl ranging from cambrian to Triassic in age,structurally controlled by domes,anticlines and second-ordered faults.They are similar to the Carlin-type gold deposits in mineral assemblage and geochemical marks,with an element association closely comparable to those of modern springs and submarine hydrothermal sediments.Organic matter may have played an important role in mineralization .The ore solution may be hydrothermally altered meteoric water developed i areas of local geothermal anomaly.     

Gold Occurrence and Ore Genesis,Yata Micro—Disseminated Gold Deposit,Guizhou,Southwest China

The mode of occurrence of gold in the Yata micro-disseminated gold deposit is ap-proached through chemical phase studies coupled with ore-dressing monitoring and micro-beam analysis.The results showed that gold occurred for the most part as ultra-microscopic particles adsorbed on the surfaces or fracture planes of pyrite and other sulphides.The proportions of gold of different occurrences were estimated solutions containing nanometer-sized gold particles were prepared following the hydrolysis-reduction procedure and the adsorption of nanometer-sized gold on ordinary sulphides and rocks was experimentally determined.It is evident that sulphides are good adsorbents of gold and this is consistent with geological observations.     

Element Geochemistry and Petrogenesis of High—K Potassic Dike Rocks in Two Types of Gold Ore Fields in Northwest Jiaodong,Shandong,China

This paper deals with the high-K,potassic dike rocks in two types of gold ore fields at Linglong and Dayigezhuang,Northwest Jiaodong.The rocks can be divided into three types.i.e.,(1) lamprophyre,(2) andesite porphyrite,and (3) dacite porphyrite,based on their geological occurrence and space-time relationship with gold mineralization.These rocks were the products of early,synchronous and late mineralization.respectively,Element geochemistry shows that variations in chemical composition of major oxides follow the general rules of magmatic fractional crystallization.The fractional crystallization of mineral phases of augite in the early stage(namely in the lamprophyre stage)and hornblende and plagioclase in the late stge(namely from the andesite-porphyrite to dacite porphyrite stage)controlled the magma evolution.The rocks are enriched in alkili and have higher K2O and lower TiO2 contents,as well as strongly enriched in large ion lithophile elements such as Ba,Sr and Rb,and LREE but strongly depleted in transition elements such as Cr and Ni,Rb is depleted relative to Sr and Ba,and Rb/Sr ratios are low.Volatile constituents are abundant.These characteristics indicate that the initial magma originated from the metamorphic subduction ocean-crust that had been intensively contaminated by crustal materials,and retrogressive metamorphism is characterized by low-degree partial melting during back-arc spreading,Varying degrees of partial melting and different emplacement enviornments may be the main causes for the evolution of the rocks and mineralization in different degrees in the two gold ore fields at Linglong and Dayigezhuang,Shandong.     

The Chahe Copper Deposit—Its Age and Genesis

The Chahe copper deposit occurs in the Early Proterozoic metamorphic series in the area of Chahe and its chalcopyrite yielded a Pb−Pb isochron age of 951±36 Ma, providing evidence for copper mineralization at the early stage of the Jinning movement. The ore-forming material came from terrestrial clastic sediments and marine volcanic eruption and the ores were deposited in a relatively open beach environment. The Jinning movement led to folding and metamorphism of country strata, as well as to the rebomilization and transport of copper, resulting in ore deposition in structurally weak locations. This deposit is a volcano-sedimentary metamorphic deposit.     

湘中锑(金)矿床成矿物质来源——Ⅱ.同位素地球化学证据

文章从碳、氢、氧、硫、铅、锶等同位素地球化学方面探讨了湘中锑金矿床的成矿物质与成矿流体来源。研究表明：湘中盆地中锑矿床的碳、硫等矿化剂主要来源于基底地层，而盆地边缘锑（金）矿床的碳、硫等矿化剂来源于深部岩浆作用；Au,Sb等成矿物质都来源于基底碎屑岩；成矿流体主要为大气降水。