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991.
左家庄金矿矿质来源于近矿地层,成矿热液为同生沉积建造水,硫化物石英脉的形成是含矿热液流体沿左旋剪切扭动构造隐蔽面充填的结果.对其主要载金矿物黄铁矿的热电性测定,表明黄铁矿为空穴型导电,该矿床剥蚀程度不大,属上部出露. 相似文献
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烂泥沟金矿是以浊积岩为容矿岩石的微细浸染型金矿。有机岩石学分析表明,矿石与围岩中干酪根类型无明显差别,同属腐泥-腐植型。与围岩相比,矿石中干酪根成熟度(R0=2.74%-3.06%)和含金性(6.15-24.8μg/g)均较高;干酪根总含金量在全岩中所占的比例是围岩高于矿石。氯仿沥青“A”的检测说明,矿石样品中可溶性有机质形成于强还原和高盐度环境,沥青质和含硫有机化合物发育。研究认为,干酪根含金性与碳的活化有关;不饱和的有机基因对金的动一定转换可能具有重要意义。 相似文献
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作者应用气液包裹体研究和热力学方法讨论了吉林省夹皮沟—金城洞绿岩区中金矿床形成的物理化学条件,分别确定了Ⅰ矿田(石(?)沟旷田)、Ⅱ矿田(夹皮沟矿田)和Ⅲ矿田(金城洞矿田)的成矿T、P、pH、Eh、fs_2、fo_2、fco_2及成矿溶液性质、成分类型、主要成矿离子Pb~(2+)、Zn~(2+)、Fe~(2+)、[AuS_3]~(3-)的浓度。 相似文献
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The 1.78 Ga Xiong'er Volcanic Province (XVP) and coeval North China giant mafic Dyke Swarm (NCDS) are the most important magmatic events occurring after the amalgamation of the North China craton (NCC). The XVP consists of 3–7 km of extrusive volcanics and some feeder dykes/sills located along the southern margin of the NCC and extending over an area > 0.06 M km2. Compositions vary from basalt to rhyolite, but are predominantly intermediate in terms of silica content. There are also minor sedimentary intercalations and pyroclastic units. The sedimentary interlayers indicate an environment changing from continental-facies to oceanic-facies up-section. The XVP is characterized by fractional crystallization from an EM I type mantle source, and both continental arc (Andean-type) and rift environments have been proposed. The NCDS is widespread in the central NCC with an outcrop area > 0.1 M km2, and are exposed at variable depths up to 20 km (deepest in the north). Dyke compositions vary from basalt to andesite and dacite, but are dominantly mafic, and comprise two series of magmatism. Previous studies revealed that the NCDS recorded assimilation and fractional crystallization of an EM I type magma source, with a minor DM contribution in the younger magmas. Both syn-collisional and intra-continental anorogenic environments have been proposed. Spatial and petrogenic correlations suggest a cogenetic relationship between the NCDS and XVP, and considered together, they define a Large Igneous Province (LIP) of > 0.1 M km2 in area and > 0.1 M km3 in volume, which is also notable for its continuous compositional range from mafic to felsic (with no gap at intermediate compositions). The petrology is explained by a common magma source that undergoes a silica-poor and iron-enriched fractionation trend at depth followed by a silica-rich and iron-poor fractionation trend in shallow-level magma conduits (dykes) and surface lavas. A mantle plume is favored as the cause of this 1.78 Ga North China LIP. 相似文献
999.
The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated
with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the
deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe
intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have
intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly
different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental
liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization
is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal
contacts with sedimentary footwall. The δ
34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement
of external S with elevated δ
34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of picrites
associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than
that of sulfide liquid expected to segregate from undepleted picrite magma. Cr-spinel and olivine are present in the Limahe
ultramafic rocks as well as in the picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble
those of the picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust,
are present in the intrusion but absent in the picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher
degrees of contamination with the upper crust than did the picrites. The results of this study permit us to suggest that the
parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging
chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide
segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage
sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent
to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying
unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose
that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills
or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second,
relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine
crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were
then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit
in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe
deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential
of economic Ni–Cu sulfide deposits. 相似文献
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