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.

Mineralogical Zonation of Wall-Rock Alteration in Jiaodong Gold Province, North China

Mineralogical zonation of wall rock alterations in Mesozoic granitoids is summarized from 18 gold deposits in Jiaodong gold province on the Asian mobile continental margin of the west circum Pacific rim. This paper deals with wall rock alterations developed around gold mineralizations of the quartz vein type in granitoids and the wall rock alteration type in granitoid basement contacts along Mesozoic fault zones trending mostly NNE SSW and NE SW. Five alteration zones are distinguished from host rock to ore zone, namely the chloritization and sericitization zone, the hematitization rutilization and microclinization zone, the quartz sericitization zone, the pyrite quartz sericitization zone and the pyrite silicification zone. The former two are outer zones marked by incomplete alteration of first mafic and then felsic minerals of the granitoids, while the later three are inner zones marked by complete alteration of both mafic and felsic minerals of the granitoids leading to retrogressive sericitization and progressive silicification with participation of ore elements. The whole process proceeds under dynamometamorphism with high fugacity of volatiles. Wall rock alteration is the intermediate link between unaltered host rock and ore mineralization both in time and space. Development of the alteration zonation and its mineral composition controls genetic type of mineralization, size and grade of the deposit and location of the ore zones.

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.

Effect of Groundwater Radiolysis on the Wall-rock Alteration of Uranium Ore Deposits

Reported for the first the in this paper are the results of simulating experimnts on theγ-irradiation-induced oxidation of Fe2+ under the physicochemical conditions tr= 200℃,P= 50 MPa,Eh= -0.1V, PH=7.2) similar to tfor under which moderate-low temperature hydrothermal uraniumdeposits are formed . Evdence shows that the effect of groundwater radiolysis m to be the majormechanism of wall-rock alteration (hematitizaton ) of hydrothermal uranium deposits.Moreover, adiscussion was made of possible dets of radiolyss of the waterrock system on wall-rock alterationsincluding argillization and decoloration of uranium ore deposits on the basis of the experimentalresults.

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.

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.

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.

Geochemical Characteristics and Significance of Major Elements, Trace Elements and REE in Mineralized Altered Rocks of Large-Scale Tsagaan Suvarga Cu-Mo Porphyry Deposit in Mongolia

The alteration types of the large-scale Tsagaan Suvarga Cu-Mo porphyry deposit mostly comprise stockwork silicification, argillization, quartz-sericite alteration, K-silicate alteration, and propylitization. The mineralized and altered zones from hydrothermal metallogenic center to the outside successively are Cu-bearing stockwork silicification zone, Cu-beating argillized zone, Cu-Mo-bearing quartz-sericite alteration zone, Cu-Mo-bearing K-silicate alteration zone, and pro- pylitization zone. The K-silicate alteration occurred in the early phase, quartz-sericite alteration in the medium phase, and argillization and carbonatization （calcite） in the later phase. Ore-bearing-altered rocks are significantly controlled by the structure and fissure zones of different scales, and NE- and NW-trending fissure zones could probably be the migration pathways of the porphyry hydrothermal system. Results in this study indicated that the less the concentrations of REE, LREE, and HREE and the more the extensive fractionation between LREE and HREE, the closer it is to the center circulatory hydrothermal ore-forming and the more extensive silicification. The exponential relationship between the fractionation of LREE and HREE and the intensity of silicification and K-silicate alteration was found in the Cu-Mo deposit studied. The negative Eu anomaly, normal Eu, positive Eu anomaly and obviously positive Eu anomaly are coincident with the enhancement of Na2O and K2O concentrations gradually, which indicated that Eu anomaly would be significantly controlled by the alkaline metasomatism of the circulatory hydrothermal ore-forming system. Therefore, such characteristics as the positive Eu anomaly, the obvious fractionation between LREE and HREE and their related special alteration lithofacies are suggested to be metallogenic prognostic and exploration indications for Tsagaan Suvarga-style porphyry Cu-Mo deposits in Mongolia and China.

An integrated ore prospecting model for the Nyasirori gold deposit in Tanzania

The Nyasirori gold deposit,located in the middle-western end of the Musoma-Mara Archean greenstone belt in Tanzania,is a tectonic altered rock type gold deposit controlled by shear tectonic zone.This work conducted high-precision ground magnetic measurements to delineate fault structures and favorable prospecting targets,utilized induced polarization(IP)intermediate gradient to roughly determine the distribution and extension of the tectonic altered zone and gold ore(mineralized)bodies,and further carried out IP sounding and magnetotelluric sounding to locate the tectonic altered zone and gold ore(mineralized)bodies.The anomalous gradient belt of the combination of positive and negative micromagnetic measurements reflects the detail of shallow surface tectonic alteration zone and gold mineralization body.Micromagnetic profile anomalies indicate the spatial location and occurrence of concealed tectonic alteration zone and gold(mineralized)ore bodies.Soil geochemical measurements indicate that the ore-forming element Au correlates well with As and Sb,and As and Sb anomalies have a good indication to gold orebodies.Based on the multi-source geological-geophysical-geochemical information of the Nyasirori gold deposit,this work established an integrated prospecting model and proposed a set of geophysical and geochemical methods for optimizing prospecting targets.

右江盆地大际山U-(Mo)矿床围岩蚀变特征及微量元素迁移规律——对区域内U、Au成生关系的指示

位于扬子地块西南缘的右江盆地,是全球第二大的卡林型Au矿(共伴生有Sb、Hg、Tl异常/矿化)矿集区,有着滇黔桂“金三角”的美誉。值得注意的是,该区除发育Au(-Sb-Hg-Tl)矿床外,还产有大量赋矿岩性和控矿构造相似的U矿床(点),成矿特色鲜明。前人对该区Au矿开展了大量研究,而U矿研究较少,对U、Au的成生关系尚不清楚。基于此,文章选取右江盆地内典型的U矿床——大际山U-(Mo)矿床为研究对象,通过开展岩矿相学研究和地球化学分析,厘定了矿化的围岩蚀变为硫化、沥青质化、磷铝锶石化、硅化和伊利石化,揭示了矿化过程中Re、Tl、Mo、U、Cd、Ni、Co、As、Sb、MREE的相对富集。蚀变矿物组合及元素迁移规律约束大际山U-(Mo)矿床中成矿物质可能来源于牛蹄塘组,成矿流体应为还原性有机流体与地表-近地表酸性、氧化性流体的混合,矿质沉淀发生在低温、酸性、还原环境中。综合分析认为,右江盆地内U、Au分布特征及矿床成因具有明显差异,二者应是不同成矿事件的产物。

宁陕县某金矿地质特征及富集规律

宁陕县某金矿地处秦岭中段南坡山地,金矿体主要赋存在燕山期NE-NNE向破碎蚀变带内的破碎蚀变岩及石英脉体中。目前,该矿正处于勘查阶段,只进行了基本的地质工作,研究程度较低。本文采用激电中梯测量和1:10000土壤化学测量圈定矿体后,通过钻探验证、槽探揭露、地质测量、取样分析等工作,查明金矿地质特征,分析成矿地质条件和矿床形成机制,概括矿物富集规律和找矿标志,为后期外围探矿和深部找矿提供真实可靠的理论依据。

胶西北新东庄金矿床蚀变岩岩石地球化学特征与成矿作用

新东庄金矿床位于招平断裂中段,矿体主要沿中生代玲珑型花岗岩与胶东群变质岩接触带展布。黄铁绢英岩是主要矿化岩石,矿体下盘玲珑型花岗岩主要发育红化蚀变,上盘胶东群变质岩发育青磐岩化蚀变。主量元素分析结果显示,红化花岗岩、黄铁绢英岩、绢英岩中K_(2)O、SiO_(2)、SO_(3)含量及LOI较原岩玲珑型花岗岩普遍增加,为带入成分,且在黄铁绢英岩、绢英岩等与矿化密切相关的岩石中增幅更大。在微量元素中,Rb、U在红化花岗岩和黄铁绢英岩、绢英岩中普遍带入。新东庄金矿床的金成矿与氧逸度、酸碱性条件的变化密切相关,金富集主要发生在还原性和偏酸性条件。

浦城杉树坞萤石矿围岩蚀变岩相学特征及矿床成因

杉树坞萤石矿近矿围岩蚀变镜下微观表现为高岭土化、高岭土绢云母化、硅化等蚀变组合,野外露头蚀变调查确定围岩蚀变分带为原岩带-构造破碎带-高岭土化蚀变带-硅化绢云母化带-萤石矿带-硅化带-构造碎裂带-另一侧的原岩带,反应矿体成矿过程为原岩中细粒黑云母二长花岗岩和花岗斑岩,在经过一系列构造运动作用下,形成碎裂化黑云母二长花岗岩、碎裂化花岗斑岩;随着张性断裂活动进一步加剧,岩石破碎成角砾形成花岗质碎裂角砾岩;含矿热液沿构造裂隙运移,通过组分的带进带出,形成高岭土化碎裂角砾岩、高岭土绢云母化碎裂角砾岩、萤石硅化岩。杉树坞萤石矿受构造运动时产生的动力破碎叠加低温热液蚀变作用而成,属于低温热液充填型萤石矿床,硅化叠加强烈高岭土化、绢云母化为最为明显的找矿标志。

辽东连山关(3075)铀矿床流体包裹体测温研究

连山关(3075)铀矿床是我国品位最好的热液铀矿床之一。为了探讨该矿床成矿模式,为矿区外围找矿提供依据,文章通过矿石矿物特征和围岩蚀变对成矿阶段进行了划分,并结合流体包裹体测温,对比研究了不同成矿阶段流体性质特征。结果显示,连山关(3075)铀矿床发育的围岩蚀变主要有绢云母化、硅化、钠长石化、绿泥石化、碳酸盐化,其中绢云母化贯穿于成矿作用的始终,硅化、钠长石化主要发生在成矿早阶段,绿泥石化、碳酸盐化主要发生在成矿晚阶段。从成矿早阶段、主成矿阶段到成矿晚阶段,流体包裹体的均一温度峰值依次为320~340℃、260~280℃和160~180℃,流体盐度峰值依次为15%~18%NaCl_(eqv)、10%~11%NaCl_(eqv)和6%~7%NaCl_(eqv),流体密度集中在区间0.8~1.0 g/cm^(3)。连山关(3075)铀矿床属于中高温、中低盐度、低密度热液铀矿床,随着流体的演化,成矿流体的温度、盐度、压力不断下降,压力的急剧下降是促使铀沉淀的重要因素;区内北西西向和北东东向断裂控矿作用明显,既是变质热液运移的通道,也是铀矿物沉淀的场所,为矿区外围找矿提供了方向。

豫西前河金矿床构造原生晕特征及其对深部找矿的指示

前河金矿床是典型构造蚀变岩型金矿床,矿体受近东西向构造控制。构造研究表明,该矿区经历了多期演化,形成近东西向、北东向、南北向等3个方向的构造,不同构造对矿体起着控制或破坏作用。F_(4)断裂为近东西向构造的典型代表,为Ⅳ号矿带的容矿构造。通过对Ⅳ号矿带进行构造原生晕分析,认为头晕元素整体以中、内带异常为主,近矿晕元素以内带异常为主,尾晕元素分布差别较大,可能与元素变异系数变化较大有关。葚沟矿段00中段83勘探线深部、石家岭矿段260中段43勘探线—45勘探线深部均具有较好的找矿前景。

滇北余家村金银多金属矿床成矿条件及模式研究

云南省宁蒗县余家村矿区地处三江成矿带东缘、宁蒗-祥云铜钼成矿带北段,矿区地质构造复杂,岩浆活动强烈,具有较好的成矿远景。然而,矿区探采工作受到一定困扰,地质找矿仍未取得突破。究其原因,主要为对矿区的成矿条件和控矿规律认识不足。为此,本文根据近年来矿区地质勘探资料,系统性地总结了矿区金银多金属矿化带的地质特征,并从地层、构造、岩浆岩以及围岩蚀变等方面剖析其成矿条件和规律,最终提炼出矿区的金银多金属矿化带(M1)的成矿模式,以期为该地区地质找矿提供理论基础和技术支撑。

甘肃北山斜沟—红柳丘井地区土壤地球化学特征及找矿远景

在斜沟—红柳丘井地区开展1∶50 000土壤测量,采集样品5 625件,粒度为4目至20目。通过样品加工分析和地球化学参数统计,对成矿元素地球化学特征进行研究,圈定单元素异常467处、组合异常3类、综合异常17处。根据异常查证评价情况对综合异常进行了分类及排序。在此基础上,结合区域地质背景、矿产资源分布情况,划分了以Au、Pb、Zn、W、Mo为主的找矿远景区5处,初步评价了其成矿潜力,指出具有找矿潜力的矿床类型为斑岩型钼矿床、蚀变岩型金矿床、火山热液型金矿床。

甘肃大店沟金矿床蚀变矿物特征与金矿化的关系

大店沟金矿床位于西秦岭成矿带上,其矿体类型为石英脉型和构造破碎带蚀变岩型。通过对该区岩石样品进行近红外光谱分析仪测试,确定大店沟金矿床围岩蚀变类型、蚀变矿物含量及特征,并讨论围岩蚀变与金矿化之间的关系。结果表明,该矿床的主要蚀变类型有绢云母化、绿泥石化、黄铁矿化、硅化及碳酸盐化。白云母、锂云母、伊利石、绿泥石等矿物与金矿化呈正相关性,蚀变矿物含量与区内揭露矿体空间位置及规模相对应,后期可作为较好的找矿标志性信息。

岷县三角地金矿成矿地质条件及成因分析

岷县三角地金矿主要矿体产出于二叠系崖下组地层石英脉中,矿体受北西西向断裂构造控制,矿石类型属含黄铁矿化石英脉型,围岩多为深灰色泥质粉砂岩。通过地质勘查结合以往地质资料对其成因分析,岷县三角地金矿矿床成因类型为中低温热液型矿床,认为该区域找矿地质条件优越,具较好找矿前景。

安徽庐江沙溪铜金矿床蚀变岩地球化学特征和金的赋存状态研究

斑岩型铜金矿床是金资源的重要来源,研究其中载金矿物(如硫化物)的种类其中的金含量是高效回收金的关键。本文通过对沙溪矿床不同类型蚀变岩和工业品位矿石开展系统的矿物学和地球化学成分研究发现,沙溪矿床中钾化蚀变更富集Si、Fe和K、贫Na,青磐岩化蚀变更富集Al和Fe、贫Ca,石英绢云母化更富集Ca和Na、贫Fe和K。矿石内主要脉石矿物为石英含量为37.65 wt%,钠长石含量为17.15 wt%,碱性长石含量为11.35wt%,白云母含量为12.87 wt%,硫化物黄铁矿和黄铜矿含量分别为1.36 wt%、1.17 wt%。金是以类质同象替换的形式存在于黄铁矿和黄铜矿中,在二者中的占比分别为5.98%、2.15%,其他类型占比为91.87%。