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11.
Alfons M. van den Kerkhof Geoffrey H. Grantham 《Contributions to Mineralogy and Petrology》1999,137(1-2):115-132
In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to 10 m in width in the normally
garnetiferous Nicholson's Point Granite, are developed adjacent to intrusive contacts with the Port Edward Enderbite and anhydrous
pegmatitic veins. Mineralogical differences between the country rock and charnockitic aureole suggest that the dehydration
reaction Bt + Qtz → Opx + Kfs + H2O and the reaction of Grt + Qtz → Opx + Pl were responsible for the charnockitization. The compositions of fluid inclusions
show systematic variation with: (1) the Port Edward Enderbite being dominated by CO2 and N2 fluid inclusions; (2) the non-charnockitized granite by saline aqueous inclusions with 18–23 EqWt% NaCl; (3) the charnockitic
aureoles by low-salinity and pure water inclusions (<7 EqWt% NaCl); (4) the pegmatites by aqueous inclusions of various salinity
with minor CO2. As a result of the thermal event the homogenization temperatures of the inclusions in charnockite show a much larger range
(up to 390 °C) compared to the fluid inclusions in granite (mostly <250 °C). Contrary to fluid-controlled charnockitization
(brines, CO2) which may have taken place along shear zones away from the intrusive body, the present “proximal” charnockitized granite
formed directly at the contact with enderbite. The inclusions indicate contact metamorphism induced by the intrusion of “dry”
enderbitic magma into “wet” granite resulting in local dehydration. This was confirmed by cathodoluminescence microscopy showing
textures indicative for the local reduction of structural water in the charnockite quartz. Two-pyroxene thermometry on the
Port Edward Enderbite suggests intrusion at temperatures of ∼1000–1050 °C into country rock with temperature of <700 °C. The
temperature of aureole formation must have been between ∼700 °C (breakdown of pyrite to form pyrrhotite) and ∼1000 °C. Charnockitization
was probably controlled largely by heat related to anhydrous intrusions causing dehydration reactions and resulting in the
release and subsequent trapping of dehydration fluids. The salinity of the metamorphic fluid in the contact zones is supposed
to have been higher at an early stage of contact metamorphism, but it has lost its salt content by K-metasomatic reactions
and/or the preferential migration of the saline fluids out of the contact zones towards the enderbite. The low water activity
inhibited the localized melting of the granite. Mineral thermobarometry suggests that after charnockite aureole genesis, an
isobaric cooling path was followed during which reequilibration of most of the aqueous inclusions occurred.
Received: 8 November 1998 / Accepted: 21 June 1999 相似文献
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西藏甲玛铜多金属矿床磁黄铁矿标型矿物学特征及其地质意义 总被引：2，自引：0，他引：2
甲玛矿床位于冈底斯成矿带东段,是西藏地区最大的铜多金属矿床之一。磁黄铁矿是甲玛矿床最常见的金属矿物之一,其标型特征不仅反映其自身形成环境,对其形成机制和矿床成因也具有指示意义。文章选取产于不同岩性中的磁黄铁矿矿石样品,利用矿相学、X射线衍射和电子探针分析等手段对磁黄铁矿的形态、成分和结构进行了分析研究。研究表明,甲玛矿床的磁黄铁矿主要分布在距离岩体中心较远的矿区远端矽卡岩和角岩中。磁黄铁矿的晶胞参数和粉晶X射线衍射曲线显示矽卡岩中的磁黄铁矿主要为高温六方磁黄铁矿,角岩中的磁黄铁矿为高温六方磁黄铁矿和低温单斜磁黄铁矿的交生体,但主要以低温单斜磁黄铁矿为主。通过对矽卡岩和角岩中的磁黄铁矿进行电子探针测试,结果显示:矽卡岩中的磁黄铁矿中w(Fe)为60.09%～60.71%,平均为60.38%,w(S)为38.18%～38.69%,平均38.35%,化学分子式为Fe_8S_9～Fe_(10)S_(11);角岩中的磁黄铁矿中w(Fe)为59.05%～59.57%,平均为59.10%,w(S)为39.28%～39.95%,平均39.59%,化学分子式为Fe_5S_6～Fe_7S_8。根据以上矿物学特征,笔者进一步探讨了该矿床磁黄铁矿的沉淀机制:炽热的岩浆热液上涌,与碳酸盐岩地层和碎屑岩地层接触发生相互作用,并有大气水的加入,使得成矿流体在角岩中先快速降温,形成高温六方磁黄铁矿和低温单斜磁黄铁矿的交生体。同时,大量的含矿热液形成,并充填于有利的成矿空间(主要为层间破碎带)沉淀成矿,形成矽卡岩矿体,然后流体在矽卡岩矿段中经历缓慢降温,形成高温六方磁黄铁矿。结合矿床地质特征和相关元素地球化学特征,认为甲玛矿床类型为斑岩-矽卡岩型。 相似文献
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A symplectite of pyrite and magnetite in the massive sulphide ore of the Mashan mine,Anhui Province,is interpreted to have been formed by their replacing earlier pyrrhotite.The compositions of pyrrhotite,pyrite and magnetite related to this texture are given by electron microprobe analysis.Such a texture is likely to be formed when the ore-forming system reaches the three-phase point of pyrrhotite,pyrite and magnetite from the pyrrhotite stability field.The very small probability for the system to reach this point could be used to account for the rare occurrence of such symplectite in natural ores. 相似文献
16.
吉林省红旗岭矿区磁黄铁矿—镍黄铁矿矿石建造特征及其成因分析 总被引：2，自引：1，他引：2
本文对红旗岭矿区磁黄铁矿－镍黄铁矿矿石建造进行了研究。并通过矿石组特征，矿物形成温度，硫、锶同位素，岩体稀土元素特征等研究，进一步论述了磁黄铁矿与镍黄铁矿的物质来源于上地幔。属于深部岩浆熔离含矿熔浆冷凝而成。 相似文献
17.
辽宁东平金矿床地质特征及找矿方向 总被引：1，自引：0，他引：1
南秦岭南部构造带具备较好的金矿成矿条件与成矿背景，是该区域规模较大金矿带.金沟矿段是黄龙金矿床最主要的组成部分，该矿段矿石中磁黄铁矿和黄铁矿发育，其中磁黄铁矿矿石是矿床中含量最高的硫化物矿石.磁黄铁矿存在两种产出状态，分别为早期形成的呈浸染状、团块状分布的磁黄铁矿与晚期形成的脉状磁黄铁矿.成分分析结果表明以单斜磁黄铁矿为主.该矿床属中-低温矿床.微量元素结果显示富Co贫Ni，与金矿化关系密切.在含金性方面，脉状产出的磁黄铁矿优于团块状分布的磁黄铁矿，且脉体越细含金性越好，因此细脉状磁黄铁矿可作为该区重要的找矿标志. 相似文献
18.
江南钨矿带高家塝钨多金属矿床矿化分带特征及其指示意义 总被引：1，自引：1，他引：0
高家塝钨多金属矿床位于江南钨矿带北部.钨矿化发育在花岗闪长斑岩与黄柏岭组接触的矽卡岩及其两侧.从岩体向外将矿石划分为:花岗闪长斑岩中细脉浸染状白钨矿矿石(类型Ⅰ)、矽卡岩中浸染状白钨矿矿石(类型Ⅱ)、角岩中脉状白钨矿矿石(类型Ⅲ)3类.高家塝矿床不同类型矿石的白钨矿和磁黄铁矿电子探针(EPMA)分析结果显示,白钨矿w(Mo)从类型Ⅱ(w(Mo)=1.34％～1.40％)→类型Ⅲ(w(Mo)=0.01％～0.17％)→类型Ⅰ(w(Mo)<0.01％)降低.从类型Ⅰ→类型Ⅱ→类型Ⅲ,磁黄铁矿中Cu、Fe元素含量降低;Zn、Co、Ni含量增高.高家塝钨矿床形成白钨矿的成矿流体从类型Ⅱ→类型Ⅲ→类型Ⅰ,氧逸度降低;形成磁黄铁矿的早期石英-硫化物阶段,类型Ⅱ的成矿流体降温速率缓慢,类型Ⅰ和Ⅲ的成矿流体发生快速冷凝作用.区域对比研究显示,高家塝矿床为贫钼白钨矿矿床,形成于还原环境. 相似文献
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