Structural controls on gold mineralisation and the nature of related fluids of the Paiol gold deposit, Almas Greenstone Belt, Brazil     

Mrcio Anselmo Duarte Ferrari  Asit Choudhuri 《Ore Geology Reviews》2004,24(3-4):173

Chemical analyses suggest that the metavolcanic rocks of the Almas Greenstone Belt (AGB), Tocantins State, Brazil have a continental affinity, possibly related to a continental rift environment. They were metamorphosed to amphibolite facies during a regional tectono-metamorphic event (D_n), retrogressed to greenschist facies assemblages and then hydrothermally altered within dextral strike–slip shear zones (D_n+1). Fracture sets related to D_n+2 intersect S_n+1.The Paiol Gold Mine is one of several mineralised zones within metabasic and meta-intermediate rocks of the AGB. It exploits shoots of sulphide–Au–quartz mineralisation that occupy dilational zones approximately perpendicular to an elongation lineation (L_n+1) within mylonitic foliation S_n+1 (S_n+1=S within the S–C fabric). The dilational zones probably formed due to dextral displacement on sinistrally en echelon C surfaces. Minor amounts of gold may have been introduced or remobilised during D_n+2.Coexisting primary and pseudosecondary fluid inclusions in mineralised quartz veins from ore shoots comprise a high-salinity three-phase type (Type II) and a lower salinity two-phase type (Type I). Homogenisation temperatures for Type II inclusions range from 200 to 410 °C and Type I from 90 to 320 °C. The inclusions and their temperature ranges are believed to reflect heat exchange and some mixing between the two fluid types under relatively constant ambient temperatures, but variable (though broadly declining) fluid temperatures. This took place late in D_n+1 in conjunction with greenschist facies retrogression and localised hydrothermally induced metasomatism.  相似文献   

引力位虚拟压缩恢复法   总被引：12，自引：7，他引：12  

申文斌 《武汉大学学报(信息科学版)》2004,29(8):720-724

提出了一种将地球表面的引力位虚拟地压缩到地球内部的一个球体表面 ,进而求解在整个地球外部空间 (包括地球边界上 )的重力位场以及重力场的方法  相似文献   

导航卫星自主定轨的算法研究及模拟结果   总被引：5，自引：2，他引：5  

刘经南  曾旭平  夏林元  赵齐乐 《武汉大学学报(信息科学版)》2004,29(12):1040-1044

讨论了利用卫星-卫星间的距离观测值建立导航卫星系统自主定轨的数学方法，并用GPS星座模拟星间观测值，采用滤波算法计算卫星的状态参数。模拟结果表明，在空间测距精度一定的情况下，自主定轨精度能高于GPS广播星历，因而能较精确地维持卫星系统的坐标框架。  相似文献   

Water pollution in gold mining industry: a case study in Roşia Montană district, Romania     

R. M. Florea  A. I. Stoica  G. E. Baiulescu  P. Capotă 《Environmental Geology》2005,48(8):1132-1136

The preliminary study of streams and rivers from the Roşia Montană area revealed that the concntration of heavy metals— Cd, Mn, Cu, Pb, and Zn—are above accepted limits. The gold extraction method is based on flotation. The most important pollution sources are mine tailings. The determinations were performed for samples collected in: April 2004, July 2004, September 2004, November 2004, February 2005 and May 2005. The highest concentrations were found for cadmium in September 2004: 0.17 mg/L; for copper in September 2004: 1.38 mg/L; for manganese in July 2004: 239.4 mg/L; for lead in May 2005: 0.54 mg/L; and for zinc in September 2004: 35.37 mg/L;. This study involved three small rivers (streams) that flow into the Mureş River and finally into the Danube River, having a great impact on human health and environmental stability in the area. In May 2005, a sample of drinking water from the mining district was also collected.  相似文献   

Geologic and geochemical study of the Picacho gold mine, California: gold in a low-angle normal fault environment     

Steven Losh  Dan Purvance  Ross Sherlock  E. Craig Jowett 《Mineralium Deposita》2005,40(2):137-155

The Picacho gold deposit, located in southeasternmost California, is a low-grade gold deposit in a nearly flat-lying denudational fault of regional extent and probable Oligocene age. The deposit is hosted by intensely fractured and faulted Mesozoic leucogranite and by chloritic augen gneiss and schist, and is overlain unconformably and in fault contact by unmineralized late Oligocene Quechan volcanic rocks. The deposit is structurally characterized by normal and normal-oblique faults of low to high dip at shallow depths in the mine, merging downward with a synchronous, low-dipping ore-stage extensional fault system (the Chocolate Mountains/Gatuna Fault) of probable Oligocene age in deeper portions of the deposit. The fault system was infiltrated during much of its active life by hot, dilute, highly exchanged meteoric water having temperatures of 170°–210° C, salinity <2 wt% NaCl equivalent and calculated δ¹⁸O_fluid between −2.6‰ and 5.2‰. This main-stage fluid precipitated quartz, pyrite, and specular hematite, accompanied by silicification and sericitization. Auriferous ore-stage pyrite was precipitated late in the fault evolution probably by mixing of reducing ore fluid with relatively oxidized main-stage fluid during regional Oligocene extension on the Chocolate Mountains/Gatuna Fault. The Picacho deposit is characterized by a gold–arsenic–antimony geochemical signature consistent with bisulfide complexing of gold in reducing fluid, in contrast with typical denudation fault-hosted base-metal-rich deposits associated with high-salinity fluids elsewhere in the southwestern United States. The deposit is overprinted by Miocene normal faults having a wide range of dips. These postore faults are associated with red earthy hematite precipitation, pyrite oxidation, and supergene enrichment of gold. Editorial handling: L. Meinert  相似文献   

Magma evolution and the formation of porphyry Cu–Au ore fluids: evidence from silicate and sulfide melt inclusions     

Werner E. Halter  Christoph A. Heinrich  Thomas Pettke 《Mineralium Deposita》2005,39(8):845-863

Silicate and sulfide melt inclusions from the andesitic Farallón Negro Volcanic Complex in NW Argentina were analyzed by laser ablation ICPMS to track the behavior of Cu and Au during magma evolution, and to identify the processes in the source of fluids responsible for porphyry-Cu-Au mineralization at the 600 Mt Bajo de la Alumbrera deposit. The combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle-derived mafic magma that contained approximately 6 wt.% H₂O and 200 ppm Cu. This magma and a rhyodacitic magma mixed in an upper-crustal magma chamber, feeding the volcanic systems and associated subvolcanic intrusions over 2.6 million years. Generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps: (1) Generation of a sulfide melt upon magma mixing in some parts of the magma chamber. (2) Partitioning of Cu and Au into the sulfide melt (enrichment factor of 10,000 for Cu) leading to Cu and Au concentrations of several wt.% or ppm, respectively. (3) A change in the tectonic regime from local extension to compression at the end of protracted volcanism. (4) Intrusion of a dacitic magma stock from the upper part of the layered magma chamber. (5) Volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber, generating a fluid with a Cu/Au ratio equal to that of the precursor sulfide. (6) Focused fluid transport and precipitation of the two metals in the porphyry, yielding an ore body containing Au and Cu in the proportions dictated by the magmatic fluid source. The Cu/S ratio in the sulfide melt inclusions requires that approximately 4,000 ppm sulfur is extracted from the andesitic magma upon mixing. This exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for S. The extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma. It appears, thus, that unusually sulfur-rich, not Cu-rich magmas are the key to the formation of porphyry-type ore deposits. Our observations imply that dacitic intrusions hosting the porphyry–Cu–Au mineralization are not representative of the magma from which the ore-fluid exsolved. The source of the ore fluid is the underlying more mafic magma, and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated. At Alumbrera, these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole. Sulfide inclusions in similar dykes of other, less explored magmatic complexes may be used to predict the Au/Cu ratio of potential ore-forming fluids and the expected metal ratio in any undiscovered porphyry deposit.Editorial handling: B. Lehmann  相似文献   

北斗三号组网卫星数据质量分析及单系统定轨精度初步评估     

曾添  贾小林  隋立芬  肖国锐  田翌君  吕志鹏 《大地测量与地球动力学》2019,39(11):1165-1170

选取2018-01-23起10 d内16个iGMAS测站观测数据，对北斗三号卫星的观测数据质量及BDS单系统精密定轨精度进行评估。初步结果表明，老信号B1I、B3I北斗三号卫星的信噪比略强于二号卫星，噪声与多路径基本相当，均在0.1 m量级，新卫星不存在星内多路径偏差。新信号B1C/L1/E1频点GPS信噪比最强，Galileo和BDS卫星相当，B2a/L5/E5a和B2b/E5b各系统基本相当；噪声及多路径方面，B1C/L1/E1频点GPS优于BDS、Galileo卫星0.1 m量级，B2a/L5/E5a和B2b/E5b各系统基本相当，均在0.1 m量级，新信号中北斗三号卫星星内多路径偏差基本消失。单系统精密定轨试验中，分别进行有/无GEO卫星策略、太阳光压模型ECOM 五/九参数策略的比较，并使用卫星激光测距数据进行独立检核。初步结果表明，有GEO卫星、ECOM五参数光压模型的定轨精度最好，C19号卫星7个重叠弧段的平均定轨精度在沿迹向、法向、径向的精度分别为32 cm、16 cm、8 cm，与试验卫星的定轨精度基本相当。  相似文献   

Status of Satellite Orbit Determination and Time Synchronization Technology for Global Navigation Satellite Systems     

ZHOU Shan-shi  HU Xiao-gong  LIU Li  HE Feng  TANG Cheng-pan  PANG Jun-yang 《Chinese Astronomy and Astrophysics》2019,43(4):479-492

In the form of satellite ephemerides and clock parameters, the space datum and system time information of one global navigation satellite system (GNSS) is transferred to users. With the continuous updating in the satellite payload such as the high-precision atomic clock, the monitoring and tracking technique such as the inter-satellite link, and in the data processing technique, the accuracy and real-time performance of the satellite ephemeris and clock error products are steadily improved. Starting from December 27th, 2018, the BeiDou Navigation System 3, or BDS-3, has provided the accurate and reliable basic positioning, navigation, and timing (PNT) service for the users in the countries within the “one belt and one road”. This paper has summarized the faced challenges of the precise orbit determination and time synchronization from the regional BDS-2 system to the BDS-3 global system, and the specific solutions at the control segment. In addition, this paper has compared the BDS with other GNSS systems in terms of technical characteristics. Finally, aiming at a higher accuracy and more reliable PNT service, the road map of precise orbit determination and time synchronization technique for the next generation navigation systems is discussed, which will provide a reference for developing the global navigation satellite systems with an even higher accuracy.  相似文献   

利用微波等离子体炬四极杆质谱在线测定稀土矿样中的多种稀土元素     

初晨  张瑛  王尚贤  周润芝  蒋涛  朱志强  卢爱民 《岩矿测试》2016,35(5):468-474

随着稀土的应用越来越广泛,开发稀土元素的快速在线检测技术已日趋成为行业发展的需求。本文以微波等离子体炬(MPT)为离子源,以四极杆质谱仪(QMS)作为质量分析器建立了一种快速、直接检测水样中稀土元素的质谱检测方法,并将其应用于分析稀土矿样中的多种稀土元素。研究表明,应用MPT-QMS测定水样中的钇、镧、铈、钕、铕五种稀土元素,检出限(LOD)可达11.0~60.5μg/L,测定范围为50~1000μg/L。当分析固体稀土矿样时,样品经酸溶处理后通过气动雾化形成气溶胶,再进行冷却干燥,气溶胶由MPT的中心管道进入等离子体中,产生稀土元素复合离子,再引入QMS中进行分析,即可以定量地测定矿样中稀土元素的含量。同一样品用电感耦合等离子体质谱(ICP-MS)进行对比实验,两者的检测结果在数量级上接近,证明了MPTQMS方法在半定量的意义下是准确、可靠的,因而这种快速的检测方法可发展成为水体中金属元素的现场分析方法,应用于环境水、生活水质量在线监测等领域。  相似文献   

南秦岭石泉-汉阴北部煌斑岩脉特征及与金矿化的关系     

韩珂  杨兴科  何虎军  高雅宁  杨龙伟  李希  杨宏宇 《地质论评》2016,62(S1):301-302

羊坪湾矿区位于南秦岭南部逆冲推覆系迎丰-搁河口推覆体。北邻留凤关-金鸡岭褶皱束,西邻扬子准地台汉南凸起,南接北大巴山弧形褶皱带。矿区出露地层由南西向北东依次为洞河群（Z2-O）和下志留统梅子垭组（S1m）。其中洞河群分布于矿区的西南部,呈北西向展布,总体北东倾,倾角15°～45°,主要为硅质板岩,板岩中局部夹薄层炭质绢云石英片岩。下志留统梅子垭组倾向北东,倾角一般15°～50°,局部倾角最高可达75o,地层沿倾向及走向具波状起伏特征。梅子垭组以绢云石英片岩、二云石英片岩、含炭绢云石英片岩为主,以及夹有少量灰岩、大理岩条带等。金矿均赋存于志留系梅子垭组二云母石英片岩和含炭二云石英片岩中,以前者为主,约占90%以上。黄龙金矿区出露地层为下志留统梅子垭组,岩性为一套巨厚的浅变质细碎屑岩系,主要为绢云石英片岩、变砂岩、含黑云母变斑晶绢云石英片岩、含炭绢云石英片岩、含石榴子石黑云母变斑晶绢云石英片岩等。其中与矿（化）体关系最为密切的岩性为含炭绢云石英片岩、含黑云母变斑晶绢云石英片岩、含石榴子石黑云母变斑晶绢云石英片岩。  相似文献