Geology and mineralization of the Dongping supergiant alkalic-hosted Au-Te deposit(>100 t Au)in Northern Hebei Province,China:A review

The Dongping deposit is the largest alkalic-hosted gold deposit in China containing>100 t of Au.This paper presents a new understanding for Dongping ore system,based on the previous studies.The mineralization originally occurred at 400-380 Ma,simultaneous with emplacement of the Shuiquangou alkaline complex,and was overprinted by the hydrothermal activity in the Yanshanian.Isotope compositions of ores indicate metals of the deposit are mainly provided by the Shuiquangou complex.Ore-forming fluids are characterized by increasing oxygen fugacity and decreasing sulfur fugacity,while tellurium fugacity increased in the Stage II-2 and decreased in Stage II-3.These systematic changes are closely related to the processes of mineral precipitation and fluid evolution.Sulfide precipitation from Stage Ⅰ to Stage Ⅱ was triggered by fluid boiling,which leads to the precipitation of Pb-Bi-Te,due to decrement of sulfur fugacity.Condensation of gas phase containing high concentration of H_2Te leads to precipitation of Te-Au-Ag minerals and native tellurium.Based on these hypotheses,this paper present a polyphase metallogenic model as follow.During the Devonian,fluids were released from alkaline magmas,which carried ore-forming materials form the surrounding rocks and precipitate the early ores.During the Jurassic-Cretaceous,fluorine-rich fluids exsolved from highly factionated Shangshuiquan granite,which extracted and concentrated Au from the Shuiquangou complex and the Sanggan Group metamorphic rocks,and finally formed the Dongping gold deposit.

Fe-bearing minerals and implications for gold mineralization for the Wangu deposit in Central Jiangnan Orogen

Hydrothermal alteration with bleaching of host rocks is the most important prospecting indicator for gold deposits in the Jiangnan Orogen Belt.The alteration has been identified as pre-ore carbonate(siderite)-sericitization and the Fe of siderite in the alteration zone is derived from the host rocks rather than fluids.In addition,such alteration decreases in intensity and width with depth and gold mineralization also occur in the non-bleached rocks,casting doubt on the reliability of the prospecting indicator.Detailed petrographic work and SEM analysis on the Wangu deposit indicate that there are two types of siderites,i.e.,Sd1 and Sd2.Among them,Sd1 grains are relatively small and distributed along the planes of unaltered host rocks,while Sd2 grains,only occurring in the altered slates,are commonly larger.Both types of siderites were altered by auriferous fluids,producing porous cores and minerals such as pyrite,quartz,and ankerite.Compared with unaltered parts,the altered parts have lower Fe,but higher U,Pb,and REE.In addition,Sd1 and Sd2 are similar in Mn,Na,V,and Sr concentrations but different in Fe and Mg.The occurrence and geochemical compositions of both siderites indicate that Sd1 could be transformed into Sd2 by pre-mineralization alteration through dissolution-reprecipitation.Chlorite is another important Fe-bearing mineral in the host rocks,and EPMA analysis suggests that it is ripidolite with relatively high Fe contents.Consequently,chlorite can also provide Fe to form the pre-ore carbonate(siderite)-sericitization.Geochemical modeling demonstrates that both ripidolite and siderite can result in sulfidation and therefore gold precipitation.As a result,this study demonstrates that pre-ore alteration with characterized bleaching is not a prerequisite for gold mineralization despite of its prominent features.Due to the presence of Fe-bearing Sd1 and chlorite,gold mineralization could still occur through sulfidation in the unaltered rocks.

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.

Alteration Typology and Geochemical Signatures of the Napélépéra Gold-Bearing Granodiorite in South-West Burkina Faso (West Africa)

The characterization of the relationships between mineralization and hydrothermal alteration is an essential element in understanding gold deposits. In south-west Burkina Faso, the Napélépéra mineralisation, the mobility of chemical elements and alteration-mineralization relationships were studied by means of selected core drilling and geochemical analyses using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and ICP-AES (Inductively coupled plasma atomic emission spectroscopy). The mineralised granodiorite is grey porphyroid with quartz, plagioclase, biotite and amphibole. It is metaluminous and located in the tholeiitic series. The Na2O + CaO versus Fe2O3 + MgO alteration diagram divides the samples according to alteration dominance. Chloritisation and carbonation are the main alterations. There is a relationship between gold mineralisation at Napélépéra and alteration, and the paragenesis of gold + pyrite ± carbonate ± silica ± sericite is the main characteristic. Carbonation is the result of fluid input in the shear corridor of the mineralised zone. The mass balance of comparative metals in the proximal and distal zones of the mineralisation shows the absence of metals, while As, Hg, Ag and Bi are strongly enriched from the distal zone to the mineralised zone. The oxides associated with the mineralisation are mainly NaO, SrO and CaO.

Metallotectic Context of the Mineralization of the Tondabo Gold Prospect(Brobo,Center of Cote d’Ivoire,West Africa)

The gold mineralization of the Tondabo prospect, located in the northern part of the Oumé-Toumodi-Fettêkro greenstone belt, is mainly hosted in the rhyodacite and to a lesser extent in the mafic volcanics (volcanic lavas and volcanoclastites). These rocks were affected by a hydrothermal alteration marked by quartz veins and veinlets associated with crystals of carbonates, sericite, epidote and sulfides. This hydrothermal alteration induced a pervasive alteration of the surrounding bodies with silicification, chloritization, carbonation and sericitization of the feldspars. The metalliferous paragenesis contains an abundant pyrite, with rare pyrrhotite and chalcopyrite. This mineralization indicates that the Tondabo gold prospect exhibits lithological control. The mineralized deposits are generally affected by a S1 schistosity oriented mainly N000-010° and minority N040-050° with a general dip of 60°-80°to the West;however with rare N-S orientations with a dip of 60°-80° to the East. The drilling intervals show that the highest gold contents are linked to the quartz-carbonates veins and veinlets, which are located in the highly deformed zones, characterizing local shear zones.

Copper and Gold Mineralization Features in Deh Bala Region—South of Takestan

The studied area is located in 30th km of Bouien-Zahra road in Saveh in southern border of Khiaraj 1:100,000 Geology map rectangle (Danesfahan) in South of Takestan of Iran. This area is a part of volcano-plutonic belt of Urumia-Dokhtar. Rocky outcrops in this area are mainly in two types of volcanic and plutonic. Volcanic Rocks with the age of Eocene are Trachyte to trachyandesite and andesite to basalt-andesite. Plutonic stones with the age of Oligo-Miocene to Miocene are in types of quartz diorite, quartz monzonite, Monzonite and Semi-acidic volcanic domes and granite aplite. Due to having dominant fault systems with trends of NW-SE and NE-SW in an intersectional manner in this area, vein-veinlets Siliciclastic sulfide mineralization can be observed in line with the same faults. Monzonite intrusive rocks are considered as host stone of these mineralizations. The information obtained from field observations and laboratory studies confirms the main alteration along with mineralization in types of silicic and pyrite, sericite, carbonate, argillic and propylitic. Mineralogy Paragenesis in the study area includes Pyrite, chalcopyrite, bornite, colitis, malachite, hematite and goethite and the most important Gang minerals including quartz, calcite, albite, sericite, kaolinite, pyrophyllite, epidote, alunite and jarosite, and according to carried out studies, copper, gold and silver are among mineralizing elements and elements such as molybdenum, cadmium, arsenic and mercury show anomalies as accompanying and guidance elements in some of the samples. The grade of copper in this area in sulfide siliciclastic veins is 1% to 3% and the grade of gold is 130 ppm and the grade of silver is reportable from 0.5 ppm to 6 ppm. Based on the geothermometry studies of fluid inclusions, homogenization temperature from 150°C?to 300°C?and the salinity grade from 4 to 5.5 percent indicate the fact that an epithermal hydrothermal system in final stages controls the mineralization of the area.

Rare-Earth Element Mobility During Ore-Forming Hydrothermal Alteration: A Case Study of Dongping Gold Deposit, Hebei Province, China

REE mobility during hydrothermal ore-forming processes has been extensively investigated in recent years and the potential of REE to provide information about ore forming processes has commonly been recognized. The Dongping gold deposit, which is located in northwestern Hebei Province, China, occurring in the inner contact zone of the Shuiquangou syenite complex, is spatially, and probably genetically, related to the syenite. The deposit was formed under the moderate to high temperature (220℃ to 320℃), weakly acidic to weakly alkaline, rather high f O 2 (lgf O 2=-30 ～- 34) environment. The REE study of the host rocks, altered wall rocks, ores and gangue minerals from the deposit suggests that the REEs have been mobilized and differentiated during K-feldspathization and silicification. The extremely altered syenite enveloping auriferous quartz vein shows positive Ce anomaly and larger LREE/HREE ratio than that of the unaltered syenite. The REE concentrations and patterns of the ores are determined by the ore types and mineral assemblages. LREE/HREE ratios in the gangue quartz and hydrothermal K-feldspars are relatively low. The most significant observation is that the gangue quartz shows significant positive Eu anomaly, whereas the hydrothermal K-feldspars show less significant or no positive Eu anomaly at all relative to the primary feldspar in the unaltered syenite. It is evident that the REEs are mobile during K-feldspathization and silicification in the ore forming process. Weak to moderate K-feldspathization caused REE mobility without apparent differentiation with the exception of extreme K-feldspathization and silicification which resulted in significant depletion of HREE and Eu and relative enrichment of Ce. The REE, Y, U, Th and Au contents of the syenite decrease as the degrees of K-feldspathization and silicification of the rocks increase towards the auriferous quartz veins. As the ores were deposited under a rather oxidized environment, Ce 4+ predominated over Ce 3+. The precipitation of the former in the form of CeO 2 or absorpted onto the secondary mineral assemblage resulted in the inconsistent removal of the REE and the relative Ce enrichment in the strongly altered rocks. In contrast, Eu was present mainly in a low valence state (Eu 2+). The geochemical differences from the other REE 3+ and much less sites in the secondary minerals to accommodate the Eu released from the original minerals resulted in the enrichment of Eu in the fluids. The mobility and differentiation of REE and the coherent mobilities of Y, U, Th and Au also support the argument that the syenite is one of the source rocks for gold mineralization. The REE contents and patterns of the altered rocks enveloping the auriferous quartz vein could be used as a guide for locating ore veins in mineral exploration.

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。

海马谷断裂北西盘金矿化蚀变带的发现及地质意义

戈塘金矿床是黔西南地区发现最早的大型金矿床之一,其金矿体均分布于区域性海马谷断裂南东盘。经近30年的断续找矿工作,海马谷断裂北西盘找矿方向及前景却依然不清。在新近的矿产地质调查工作中,在海马谷断裂北西盘,通过地电化学测量提取Au元素峰值为179.0×10^(-9),经异常查证发现荞地坡金矿化蚀变带,该金矿化蚀变带受控于下三叠统嘉陵江组一段与二段岩性突变界面,呈似层状产出,沿走向延伸1.2 km,厚0.8~2.0 m,含金品位为0.50×10^(-6)~0.82×10^(-6)。其发现过程折射出地电化学测量的引入对戈塘地区金矿找矿起到积极促进作用;也拓展了该地区找矿空间,分析认为在海马谷断裂北西盘深部有利岩性组合段与北东向构造叠加部位具有较好的金矿找矿前景。

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。

On the Genesis of the Super-large Baguamiao Gold Deposit in Fengxian County, Shaanxi Province

The Baguamiao gold deposit in Fengxian County, Shaanxi Province, is a recentlyexplored super-large gold ore deposit. A comprehensive and deep-going study has revealedthat it is a polygenetic deposit: early-stage mineralization due to shearing, middle-stagemineralization due to hydrothermal alteration, and late-stage mineralization due toweathering, leaching and concentration at shallow depths. Shearing played a dominant role inthe formation of gold orebodies.

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.

造山型金矿构造控矿作用

造山型金矿具有重要经济价值,其成矿理论研究对全球金矿勘查和开采具有重要意义。为了更好的理解挤压和伸展背景下深成-中成-浅成造山型金矿成矿过程中控矿断裂形成过程、构造控制流体流动、流体就位机制以及矿化样式之间的关系,本文系统综述了岩石破裂原理、挤压和伸展体制断裂网络结构,全面梳理全球不同构造体制和成矿深度造山型金矿的构造控矿样式、矿脉几何学和蚀变矿化网络结构,取得以下认识:(1)在挤压背景下,深成金矿通常受韧-脆性逆冲剪切带控制,发育窄蚀变带、大脉状和层压状矿石以及黑云母-角闪石-磁黄铁矿等蚀变矿化组合;中成金矿受脆-韧性逆冲剪切带、褶皱转折端的滑脱空间和里德尔剪切派生裂隙控制,发育窄-中等宽度蚀变带、层压状和网脉状矿石以及绿泥石-方解石-绢云母-黄铁矿化蚀变矿化组合;浅成金矿受脆性剪切带和次级毛细裂隙控制,发育宽蚀变带、角砾状和浸染状矿石以及绢云母-碳酸盐-硫化物(黄铁矿、毒砂)等蚀变矿化组合。研究表明上述不同成矿深度金矿构造-蚀变-矿化差异由构造、流体压力、水岩反应强度和岩石抗张强度等共同控制,流体就位和矿质沉淀机制由深部的强构造流体互馈、弱水岩反应强度向浅部的弱构造流体互馈、强水岩反应强度转换。(2)在伸展背景下,深成金矿通常受韧-脆性张剪断裂带控制,发育窄蚀变带、大脉状矿石以及黑云母-角闪石-斜长石-磁黄铁矿等蚀变矿化组合;中成金矿受脆-韧性张剪断裂带控制,发育窄-中等宽度蚀变带、断层充填脉和网脉状矿石以及绢云母化-硅化-绿泥石化蚀变矿化组合;浅成金矿受脆性断层角砾破碎带控制,发育宽蚀变带、角砾状和浸染状矿石以及绢云母-碳酸盐-硫化物(黄铁矿、毒砂)等蚀变矿化组合。伸展体制控矿构造多为先存断裂改造和再活化,当先存断裂优选定向时断裂发生再活化,成矿流体以充填断裂成矿为主,当先存断裂差异定向时流体压力驱动水力破裂形成新的断裂并改造先存构造。造山型金矿构造控矿研究已由传统的二维空间定性精细刻画逐渐向三维空间定量可视化拓展。

胶西北大尹格庄金矿床与夏甸金矿床差异性研究

大尹格庄金矿床和夏甸金矿床均分布于招平断裂中段,但二者在赋矿围岩岩性与化学成分、矿石特征、蚀变岩与蚀变矿物特征等方面存在显著差异。与夏甸金矿床相比,大尹格庄金矿床的招平断裂主裂面断层泥颜色浅,厚度小;玲珑型花岗岩含SiO_(2)、K_(2)O相对较低,含Al_(2)O_(3)、CaO、MgO、TFe_(2)O_(3)相对较高,且少见变质岩残留体;红化蚀变规模和强度较高;金矿化主要产于蚀变的玲珑型花岗岩围岩中,属典型蚀变岩型金矿床,矿石银含量较高,且常见菱铁矿。与大尹格庄金矿床相比,夏甸金矿床的招平断裂主裂面断层泥颜色黑,厚度大;矿体上盘变质岩中见有大理岩夹层;玲珑型花岗岩中常见变质岩残留体;暗灰色矿石中保留有变片麻状构造和变条带状构造,空间和成因上与变质岩关系密切,常见磁黄铁矿化;蚀变岩中见含钨金红石及白钨矿化,局部还见有石英脉型金矿化;黄铁绢英岩中SiO_(2)、Al_(2)O_(3)含量较低,K_(2)O、Na_(2)O、CaO、MgO含量较高,红化蚀变花岗岩中K_(2)O含量低于新鲜玲珑型花岗岩。赋矿围岩岩性差异及对成矿的制约是导致大尹格庄金矿床与夏甸金矿床差异性的关键。根据电化学成矿机制,夏甸金矿床成矿元素主要来自矿体上盘变质岩围岩,而大尹格庄金矿床成矿元素主要有2种来源,即胶东群变质岩和玲珑型花岗岩。

胶东大尹格庄金矿床成矿过程数值模拟及其找矿意义

大尹格庄金矿床的形成涉及到构造变形、流体活动、热量传递和水岩反应等过程的相互耦合作用。利用FLAC3D数值模拟软件,结合现代矿化率概念,开展了大尹格庄金矿床力—热—流—化耦合的数值模拟,以探讨断裂、体积形变与化学过程耦合对金矿体就位的控制作用。研究结果表明:正体积应变、流体汇聚和金析出量(负矿化率)的高值区均位于控矿招平断裂倾角由陡倾向缓倾转换部位以及断裂局部起伏部位,与金矿体的实际空间分布相吻合,反映出成矿流体更多地汇聚、停留在这些部位,并发生强烈的化学反应,引起金的沉淀析出。这种多物理—化学过程在相同部位的耦合可能是控制大尹格庄金矿床形成的关键因素,基于该成矿规律,推测大尹格庄金矿区深部具有较大的成矿潜力。

蚀变岩型低品位金矿中金的赋存状态量化研究

蚀变岩型金矿是一种重要的金矿石类型。采用化学分析、X射线衍射(XRD)、工艺矿物学参数自动分析系统(BPMA)、扫描电子显微镜(SEM)、X射线能谱(EDS)等技术,对胶东地区新立蚀变岩型金矿石中金的赋存状态进行量化研究。结果表明,矿石金品位为2.2 g/t,金属硫化物主要为黄铁矿(9.42%),含少量方铅矿(0.34%)和微量黄铜矿(0.05%)等;脉石矿物主要为石英(57.49%)和绢云母(23.31%),含少量钾长石(5.13%)等。金矿物为金-银互化物,其中银金矿占85.33%、金银矿占13.84%、自然金占0.83%;金矿物平均成色为620.8‰;载金矿物以黄铁矿为主,与黄铁矿存在镶嵌关系的金矿物占有率高达96.42%;金矿物在0~2 mm矿石综合样中以包裹金、粒间金为主,含少量裂隙金,其占有率分别为34.81%、34.73%和11.01%,并可见裸露连生金(19.39%)和微量单体金(0.06%);金矿物粒度分布不均匀,粗粒金(>74μm)、中粒金(74~37μm)、细粒金(37~10μm)、微粒金(<10μm)的占有率分别为30.56%、12.96%、46.84%和9.64%;黄铁矿的嵌布粒度较粗,主要呈中粒—粗粒嵌布,易于解离,有利于浮选。研究表明,浮选富集黄铁矿等硫化物可以有效富集金矿物,对精矿再磨,有利于金的回收;同时应注意对粗粒金的回收。

甘肃流沙沟金矿床围岩蚀变特征及其与金矿化的关系

流沙沟金矿床位于甘肃省南东部的李子园金多金属矿田内。通过岩矿鉴定和矿物短波红外光谱分析确定了流沙沟金矿床围岩蚀变类型、含量及特征,围岩蚀变主要包括硅化、黄铁绢英岩化、黏土化、碳酸盐化、绿泥石化。定量探讨了围岩蚀变与金成矿之间的关系,认为金矿化强度与绢云母、绿泥石、蒙脱石等蚀变矿物含量呈正相关性,且与较短的绢云母Al-OH波长和较高的伊利石光谱成熟度关系密切,可作为有效找矿标志。

龙门山造山带北段黄泥坪金矿床蚀变矿化特征与SWIR勘查应用研究

黄泥坪金矿床位于扬子地块西北缘,是龙门山造山带北段新发现的一个重要的中型金矿床,研究程度较低,蚀变矿化分布特征和矿床成因仍不清楚,需要新的勘查方法和思路开展下一步找矿工作。基于详细的矿床地质和短波红外光谱(SWIR)研究,发现黄泥坪金矿床的围岩蚀变主要有黄铁矿化、毒砂化、白云母化、硅化和碳酸盐化,白云母通常呈细小鳞片状分布于毒砂和黄铁矿的周围,金主要以不可见金的形式存在于毒砂和黄铁矿中。汉树沟、山关石、柳树坪和石罐子4个矿段应属同一成矿系统,其中汉树沟和山关石矿段的蚀变矿化期次可分为早期变质成矿期和晚期热液脉成矿期,变质成矿期包括石英多金属硫化物阶段和浸染状毒砂-黄铁矿阶段,热液脉成矿期包括石英-方解石粗脉阶段和毒砂-黄铁矿-方解石细脉阶段。变质成矿期发生了第一次金矿化,热液脉成矿期发生了第二次金矿化。SWIR勘查应用研究发现,矿体上盘千枚岩和下盘变质砂岩中发育较多Al–OH吸收峰位值较大的变质成因多硅白云母,而矿化部位则主要发育Al–OH吸收峰位值较小的热液白云母,Pos2200≤2202.5nm可作为热液白云母族矿物与变质成岩白云母族矿物或者二者混合相(指变质成岩白云母族矿物占主导,含有部分热液白云母族矿物)的大致界线。同时Pos2200≤2202.5 nm,且IC值为1.0~1.5可作为黄泥坪矿床新的勘查指标。本研究可以为认识龙门山北段浅变质沉积岩容矿的金矿床成矿规律和找矿勘查提供新的科学依据。