Domainal fabrics of hematite in schistose,shear zone-hosted high-grade Fe ores: The product of the interplay between deformation and mineralization

Schistose high-grade hematite orebodies (>64 wt % Fe) in the Iron Quadrangle, Minas Gerais, were formed in shear zones by hydrothermal alteration of the Paleoproterozoic Cauê BIF during the Transamazonian orogenesis. The ore is comprised of platy hematite (specularite) grains that define the foliation and overprint a relict banded martite-hematite fabric resembling, at first sight, a mylonite. The EBSD analyses of a m-scale schistose orebody from the Pau Branco mine show that specularite grew as elongated plates with the (00.1) plane parallel to the foliation. The population of the measured grain aspect ratio (GAR) is homogenous in different scales, and the longest axes of the crystals align with the stretching lineation (L//X) building continuous domains, or anastomose around stretched iron oxide aggregates and rootless fold hinges. The pole figure of the (00.1) plane shows usually a maximum centered on the pole of the foliation Z often elongated on a girdle perpendicular to the lineation L. The {10.4} pole figure has the configuration of a symmetric cleft girdle and the corresponding {11.0} and {10.0} pole figures present well developed girdles parallel to the foliation with an elongated maximum centered on X. Microstructures associated with crystal-plastic behavior and dynamic recrystallization are missing and the fabric of the orebody probably results from precipitation of strain-controlled oriented hematite plates and anisotropic syntaxial growth of favorably oriented grains with the intervention of hydrothermal fluids during Fe enrichment. The shear zone provided pathways for the percolation of mineralizing fluids under temperatures that varied from 140 to 350 °C or higher, under ductile or ductile–brittle conditions. The orthorhombic fabric and CPO (crystallographic preferred orientation) of the ore nevertheless contrast with the asymmetry of simple shear as observed in the torsion experiments by Siemes et al., 2010, Siemes et al., 2011, probably due to volume loss and possibly a flattening component of deformation in the ore zone.     

宽成分谱系岩墙群的岩石成因及其构造与成矿意义

在综述国际上为数不多的宽谱系岩墙群（WSDS）研究实例的基础上,以太行山板内造山带中的岩基后岩墙群为例,详细论证了WSDS的形成机制,并简要讨论其构造与成矿意义。研究认为,①WSDS是一类非常特殊的岩石组合,其岩石组成的多样性主要取决于岩浆起源,因而不同于已知的其他火成岩组合;②WSDS直接的构造指向是造山带岩石圈拆沉作用;③WSDS的产生必须有大规模流体活动的参与,因而是成矿作用的指示器;④岩浆系统是一种复杂性动力系统。在理想系统的框架下,由WSDS识别出的许多成因信息是相矛盾的。但是,在复杂系统的框架下,这些信息可以得到整合解释;⑤板内造山作用是一种特殊类型的造山作用,与板缘构造力没有直接的联系。WSDS同样适用于板内与板缘2种造山类型,具有普适性,都与岩石圈加厚拆沉有关。     

Polymetallic Mineralization at the Suttsu Vein-type Deposit, Southwestern Hokkaido, Japan

Abstract. The Suttsu polymetallic vein-type deposit, hosted by tuff, tuff breccia and shale of the Miocene Kunnui Formation and propylitized hornblende-augite andesite, is located in southwestern Hokkaido, Japan. It has been exploited and explored for Cu, Pb, Zn and Ag until 1962.
In this study, we examined K-Ar ages, ore mineralogical characteristics and fluid inclusions to obtain new data for the deposit.
The K-Ar ages on sericite indicate that the polymetallic mineralization occurred in Late Miocene (8.1–5.7 Ma). The polymetallic banded ore from the Ohkubo vein is characterized by an abundance of Au, Ag, Sn, Bi, in, Se and Te. These metals are mainly ascribed to electrum (30.3–37.8 atom% Ag), Se-bearing pavonite (8.5–9.5 wt% Se), gustavite-lillianite solid solution, Se-bearing bismuthinite (5.0–5.3 wt% Se), kawazulite, cassiterite, Sn-bearing chalcopyrite (3.3–4.2 wt% Sn), In-bearing stannite, stannite-chalcopyrite solid solution, and In- and Sn-bearing sphalerite (2.6–8.4 wt% In and 1.8–4.3 wt% Sn), occurring in narrow bands of the ore. The In- and Sn-bearing sphalerite likely forms a sphalerite-roquesite-stannite solid solution with the contents of roquesite and stannite being about 2–9 and 2-A mole%, respectively. Temperatures and salinities (in wt% NaCl equiv.) of the ore fluids are estimated to be 180-250C and 3–4 wt%, respectively. The Sn-bearing chalcopyrite therefore probably precipitated metastably. The geologic and mineralogical features suggest that pre-Tertiary basement rocks rich in organic material underlie the Miocene Kunnui Formation nearby the deposit and that they contributed to local and temporary reduction of magnetite-series magmas favorable for the early stage tin-polymetallic mineralization.     

河南灵宝小秦岭金矿带矿化分带特征

小秦岭矿化带近东西向展布有5个金矿化宫集带（亚矿带）。其中以文峪-杨砦峪亚矿带矿脉密度最大，矿床数量最多。全区发育有两类金矿化，即含金石英脉型与蚀变岩型，两者空间发育具互补性特点以及一定的分带趋势。全区自西向东，石英脉型矿化所占比重渐减，蚀变岩型矿化逐增，至东部雪家山岩体以东则形成一些蚀变岩型小型矿床，垂向分布上，含金石英脉型矿化多在浅部；蚀变岩型矿化则多发育于深部。     

基于ASTER与Sentinel-2A融合数据的云南普朗铜矿化蚀变信息提取

云南普朗铜矿区是我国提高战略性金属矿产铜矿资源的主要潜力地段,该矿区位于多云多雨山地高原区,采用传统地面调查方法开展找矿勘查工作受限较大,而遥感技术可在其中发挥重要作用。鉴于此,本研究选取ASTER和Sentinel-2A多光谱遥感数据,在光谱协同统一两种数据源的地表反射率基础上,采用高通滤波(High-Pass Filtering,HPF)的融合方法兼顾两种数据在短波红外波段和可见光近红外波段的优势,获取了具有高空间分辨率和高光谱保真度的ASTER-Sentinel-2A融合数据集;进而利用"比值+主成分分析法"与"主成分分析+能谱-面积法",开展了普朗铜矿区矿化遥感蚀变信息识别,并通过深入分析及野外验证,提出了对普朗铜矿蚀变信息分布特征及找矿潜力地带的新认识:(1)在原蚀变填图工作中判定为青磐岩化带的东部区域,重新进行了蚀变带的划分;(2)东部区域中新划分的钾化硅化带和绢英岩化带,具有较大找矿潜力。本研究可为普朗铜矿找矿勘查提供参考。     

月山地区铜成矿作用的同位素地球化学研究

月山地区矽卡岩型和热液脉型铜矿床氢、氧、硫、铅、和硅笔同位素组成及演化的特征显示，区内具工业价值铜矿的成矿物质主要由闪长质岩浆经熔－流分离作用提供，主要成 在放阶段的成矿热液以岩浆水为主，地矿中晚期大气降水混入量逐渐增多，三叠系和部分前三叠系提供了部分硫源和少量成矿物质。     

温度对武夷山不同海拔土壤有机碳矿化的影响

采用碱吸收法测定武夷山不同海拔土壤分别在15℃、25℃、35℃下培养35d时土壤有机碳矿化速率及矿化量的变化．结果表明,土壤有机碳矿化速率随培养时间延长而逐渐降低,尤以培养3d～7d时下降最为明显．各海拔土壤累积矿化量均随培养温度升高而逐渐增加．培养35d时15℃和35℃下土壤累积矿化量随海拔升高而增加,但25℃下黄红壤的累积矿化量高于红壤和黄壤而低于山地草甸土．各培养温度下,土壤有机碳平均矿化速率均以山地草甸土最高,红壤最低．而对于各海拔土壤,不同温度下土壤有机碳平均矿化速率大小顺序为：15℃〈25℃〈35℃．培养3d时温度为15℃／25℃黄壤的Q10值显著高于其他海拔土壤（P〈0．05）,但培养35d时15℃／25℃下的土壤Q10值以黄红壤的最高．培养3d和35d时,25℃／35℃下不同海拔土壤Q10值差异均不显著（P〉0．05）．根据土壤平均矿化速率计算的Q10值在温度范围为15℃／25℃时以黄壤的最高,但25℃／35℃时红壤的Q10值最大．     

浅析库车前陆盆地水文地质条件与铀成矿作用

根据库车前陆盆地水文地质条件,分析了地下水的铀成矿作用,并通过热力学计算等方法,对水中铀的存在形式及铀的溶解、迁移和沉淀富集过程作了较为详细的论述,阐明了盆地水化学及铀水文地球化学环境,并提出了成矿有利地段和有利层位。     

北衙金矿多期热液成矿作用识别:来自地质、岩相学、流体包裹体和H-O-S同位素证据

北衙超大型金矿床是三江特提斯成矿域中喜山期斑岩-矽卡岩型矿床的典型代表,长期以来大量研究均围绕斑岩-矽卡岩成矿作用开展并取得了丰硕成果,然而对于北衙金矿是否存在多期热液成矿作用尚不明确。本次研究基于详细野外调查、岩相学与矿相学研究,流体包裹体显微测温及成分分析、H-O-S同位素分析等多种手段,识别了北衙金矿成矿晚期存在新一期热液成矿事件。主要证据如下:(1)野外调查发现北衙金矿发育NW向陡倾断裂控制的石英多金属硫化物脉,其切割矽卡岩矿体与矽卡岩晚期石英硫化物矿脉;(2)本次研究矿脉中原生流体包裹体类型主要为富CO_2三相水溶液包裹体、含CO_2三相水溶液包裹体及气液两相水溶液包裹体,而矽卡岩晚期硫化物脉中除上述三种类型外还发育含子晶三相水溶液包裹体;(3)成矿流体均一温度分布范围为204～426℃,盐度为1.0%～14.2%NaCleqv,整体表现为中高温、中低盐度的NaCl-CO_2-H_2O流体体系,而矽卡岩晚期硫化物脉成矿流体体系具有中温、中高盐度的特征;(4)该矿脉中石英的δ~(18)O、δD范围分别为7.5‰～9.4‰与-102.0‰～-75.0‰,指示岩浆水来源,而矽卡岩晚期硫化物脉具有岩浆水和大气水混合来源。本次研究的多金属硫化物矿脉δ~(34)S值范围为-0.97‰～1.40‰,与矽卡岩期和矽卡岩晚期硫化物脉中黄铁矿S同位素一致,表明多期矿化成矿物质均具有幔源贡献。结合北衙矿集区成岩成矿动力学背景,推测始新世大规模地壳拆沉、软流圈上涌导致的强烈的壳幔相互作用可能是北衙金矿多期成矿作用的诱因。     

贵州西北部基性侵入岩锆石U-Pb年代学、岩石地球化学特征 及其与铅锌成矿关系初探

贵州西北部发育多处基性侵入岩,总体规模较小(约0.25 Km2),多沿深大断裂侵位,出露于铅锌矿点外围,本文对猫猫厂、凉山两处矿点附近的儿马冲和白岩庆两地小型基性侵入岩进行了重点研究。侵入岩主要岩性为细粒辉长岩,造岩矿物主要为拉长石、普通辉石。SiO2范围为49.60-51.09 wt%,MgO从3.88-4.27 wt %,TiO2为3.69-3.85 wt %。LA-ICP-MS锆石U-Pb定年结果为268.3±7.4 Ma,显示岩浆侵位于二叠纪。基性侵入岩的微量元素蛛网图呈OIB型特征,富集大离子亲石元素（LILE）、轻稀土元素（LREE）,亏损重稀土元素（HFEE）,相对亏损高场强元素（Nb,Ta）,有Sr、Y亏损,Pb富集。(87Sr/86Sr)i范围0.706749～0.707069,(143Nd/144Nd)i范围0.512313～0.512363,εNd(t)范围0.2～1.2;源区熔融深度处于石榴石橄榄岩相深度,可能经历了1-3 %的部分熔融,处于亏损石榴石二辉橄榄岩相向原始石榴石二辉橄榄岩相的过渡区。成岩过程中发生了单斜辉石、斜长石等矿物分离结晶,受到了有限的地壳混染作用,未经历明显的AFC过程。地壳物质在地幔源区中的加入可能是造成地幔富集的主要原因。侵入岩与成矿作用之间的关系,主要通过两方面所表现。一方面是二者间构造活动上的耦合性。另一方面是基性岩在成矿过程中可能发挥了重要的化学屏障层作用。