The Kunavaram alkaline complex is a NE-SW trending elongate body located along a major lineament, the Sileru Shear Zone (SSZ) that is regarded as a Proterozoic suture related to Indo-Antarctica collision. The complex is hosted within migmatitic quartzofeldspathic gneisses, mafic granulites retrogressed to amphibolites, and quartzites. The structural evolution of the country rocks and the alkaline complex are similar. The first phase of deformation, D1, produces a pervasive segregation banding (S1) in all rock units within and outside the complex. A second deformation phase D2 isoclinally folded S1 along subvertical axial planes with shallow plunging axes. F2 isoclinal folds are ubiquitous in the country rocks and the eastern extremity of the complex. In the interior of the alkaline body, D2 strain decreases and S1 is commonly subhorizontal. While amphibolite to granulite facies conditions prevailed during deformation, post-D2 annealing textures testify to persisting high grade conditions. In the west, a NNE-SSW trending dextral shear zone with strike-slip sense (D3) truncates the complex. Within this shear zone, quartzofeldspathic country rocks are plastically deformed, while hornblende-K-feldspar assemblages of the complex are retrogressed to biotite and plagioclase. Warping related to D3 shears also resulted in fold interference patterns on the subhorizontal S1 foliation in low D2 strain domains. Based on its steep dip, north-easterly trend, and non-coaxial nature with dextral strike-slip sense, the D3 shear zone can be correlated with the SSZ. Since this shear zone, i.e., the SSZ, is not associated with primary igneous fabrics and resulted in solid state deformation of the complex, it cannot be considered as a conduit for alkaline magmatism, but is probably responsible for the post-tectonic disposition of the pluton. 相似文献
Weights of evidence (WofE) modeling usually is applied to map mineral potential in areas with large number of deposits/prospects. In this paper, WofE modeling is applied to a case study area measuring about 920 km2 with 12 known porphyry copper prospects. A pixel size of 100 m × 100 m was used in the spatial data analyses to represent in a raster-based GIS lateral extents of prospects and of geological features considered as spatial evidence. Predictor maps were created based on (a) estimates of studentized values of positive spatial association between prospects and spatial evidence; (b) proportion of number of prospects in zones where spatial evidence is present; and (c) geological interpretations of positive spatial association between prospects and spatial evidence. Uncertainty because of missing geochemical evidence is shown to have an influence on tests of assumption of conditional independence (CI) among predictor maps with respect to prospects. For the final predictive model, assumption of CI is rejected based on omnibus test but is accepted based on a new omnibus test. The final predictive model, which delineates 30% of study area as zones with potential for porphyry copper, has 83% success rate and 73% prediction rate. The results demonstrate plausibility of WofE modeling of mineral potential in large areas with small number of mineral prospects. 相似文献
Abstract. The Batu Hijau porphyry Cu‐Au deposit, Sumbawa Island, Indonesia, is associated with a tonalitic intrusive complex. The temperature‐pressure condition of mineralization at the Batu Hijau deposit is discussed on the basis of fluid inclusion microthermometry. Then, the initial Cu‐Fe sulfide mineral assemblage is discussed. Bornite and chalcopyrite are major copper ore minerals associated with quartz veinlets. The quartz veinlets have been classified into ‘A’ veinlets associated with bornite, digenite, chalcocite and chalcopyrite, ‘B’ veinlets having chalcopyrite bornite along vuggy center‐line, rare ‘C’ chalcopyrite‐quartz veinlets, and late ‘D’ veinlets consisting of massive pyrite and quartz (Clode et al., 1999). Copper and gold mineralization is associated with abundant ‘A’ quartz veinlets. Abundant fluid inclusions are found in veinlet quartz consisting mainly of gas‐rich inclusions and polyphase inclusions throughout the veinlet types. The hydrothermal activity occurred in temperature‐pressure conditions of aqueous fluid immiscibility into hypersaline brine and dilute vapor. The halite dissolution (Tm[halite]) and liquid‐vapor homogenization (Th) temperatures of the polyphase inclusions in veinlet quartz range from 270 to 472d?C and from 280 to 454d?C, respectively. The estimated salinity ranges from 36 to 47 wt% (NaCl equiv.). The apparent pressures lower than 300 bars are estimated to have been along the liquid‐vapor‐halite curve for the fluid inclusions having the Th lower than the Tm that trapped the brine saturated with halite, or at slightly higher pressure relative to liquid‐vapor‐halite curve for the fluid inclusions having the Th higher than the Tm that trapped the brine unsaturated with halite. The actual temperature and pressure during the hydrothermal activity at the Batu Hijau deposit are estimated to have been around 300d?C and 50 bars. At such temperature‐pressure conditions, the principal and initial Cu‐Fe sulfide mineral assemblages are thought to be chalcopyrite + bornite solid solution (bnss) for the chalcopyrite‐bearing assemblage, and chalcocite‐digenite solid solution and bnss for the chalcopyrite‐free assemblage. 相似文献
Abstract. Evolution of hydrothermal system from initial porphyry Cu mineralization to overlapping epithermal system at the Dizon porphyry Cu‐Au deposit in western central Luzon, Zambales, Philippines, is documented in terms of mineral paragen‐esis, fluid inclusion petrography and microthermometry, and sulfur isotope systematics. The paragenetic stages throughout the deposit are summarized as follows; 1) stockwork amethystic quartz veinlets associated with chalcopyrite, bornite, magnetite and Au enveloped by chlorite alteration overprinting biotite alteration, 2) stockwork quartz veinlets with chalcopyrite and pyrite associated with Au and chalcopyrite and pyrite stringers in sericite alteration, 3) stringer quartz veinlets associated with molybdenite in sericite alteration, and 4) WNW‐trending quartz veins associated with sphalerite and galena at deeper part, while enargite and stibnite at shallower levels associated with advanced argillic alteration. Chalcopyrite and bornite associated with magnetite in quartz veinlet stockwork (stage 1) have precipitated initially as intermediate solid solution (iss) and bornite solid solution (bnss), respectively. Fluid inclusions in the stockwork veinlet quartz consist of gas‐rich inclusions and polyphase inclusions. Halite in polyphase inclusions dissolves at temperatures ranging from 360d?C to >500d?C but liquid (brine) and gas (vapor) do not homogenize at <500d?C. The maximum pressure and minimum temperature during the deposition of iss and bnss with stockwork quartz veinlets are estimated to be 460 bars and 500d?C. Fluid inclusions in veinlet stockwork quartz enveloped in sericite alteration (stage 2) consist mainly of gas‐rich inclusions and polyphase inclusions. In addition to the possible presence of saturated NaCl crystals at the time of entrapment of fluid inclusions that exhibit the liquid‐vapor homogenization temperatures lower than the halite dissolution temperatures in some samples, wide range of temperatures of halite dissolution and liquid‐vapor homogenization of polyphase inclusions from 230d?C to >500d?C and from 270d?C to >500d?C, respectively, suggests heterogeneous entrapment of gaseous vapor and hypersaline brine. The minimum pressure and temperature are estimated to be about 25 bars and 245d?C. Fluid inclusions in veinlet quartz associated with molybdenite (stage 3) are dominated by gas‐rich inclusions accompanied with minor liquid‐rich inclusions that homogenize at temperatures between 350d?C and 490d?C. Fluid inclusions in vuggy veinlet quartz associated with stibnite (stage 4) consist mainly of gas‐rich inclusions with subordinate polyphase inclusions that do not homogenize below 500d?C. Fluid inclusions in veinlet quartz associated with galena and sphalerite (stage 4) are composed of liquid‐rich two‐phase inclusions, and they homogenize into liquid phase at temperatures ranging widely from 190d?C to 300d?C (suggesting boiling) and the salinity ranges from 1.0 wt% to 3.4 wt% NaCl equivalent. A pressure of about 15 bars is estimated for the dilute aqueous solution of 190d?C from which veinlet quartz associated with galena and sphalerite precipitated. In addition to a change in temperature‐pressure regime from lithostatic pressure during the deposition of iss and bnss with stockwork quartz veinlets to hydrostatic pressure during fracture‐controlled quartz veinlet associated with galena and sphalerite, a decrease in pressure is supposed to have occurred due to unroofing or removal of the overlying piles during the temperature decrease in the evolution of hydrothermal system. The majority of the sulfur isotopic composition of sulfides ranges from ±0 % to +5 %. Sulfur originated from an iso‐topically uniform and homogeneous source, and the mineralization occurred in a single hydrothermal system. 相似文献
A thick sequence of mafic-ultramafic rocks, occurs along a major shear zone (Phulad lineament), running across the length of Aravalli Mountain Range for about 300 kms. It has been suggested, that this sequence may represent a fragment of ophiolite or a rift related metavolcanic suite made up of basalts and fractionated ultramafics. The geological and tectonic significance of the complex is assessed using field relationships, petrography and geochemistry. Structurally, the lowest part of the complex comprises a discontinuous band of plastically deformed harzburgite (mantle component) followed by layered cumulus gabbroic rocks (crustal component). A complex of non-cumulus rocks comprising hornblende schists, gabbros, sheeted dykes and pillowed basalts structurally overlies layered gabbros. Huge bodies of diorite intrude volcanics.
Geochemical classification suggests that all non-cumulus mafic rocks are sub-alkaline basalts except one variety of dykes which shows mildly alkaline character. The sub-alkaline rocks are tholeiite to calc-alkaline with boninite affinity. Tectono-magmatic variation diagrams and MORB normalised patterns suggest a fore arc tectonic regime for the eruption of these rocks.
The mafic rocks of Phulad Ophiolite Suite are zoned across the strike in terms of their distribution from west to east. The hornblende schists and basalts are exposed at the westernmost margin followed by gabbros and dykes. The alkaline dyke occurs at the easternmost part. The rocks of Phulad suite are juxtaposed with shallow water sediments in the east followed by platformal sediments and then continental slope sediments in the further east indicating gradual thickening of the crust from west to east and an eastward subduction. The geochemical interpretation presented in this study, together with discussion of lithological association is used to decipher the tectonic evolution of the Mesoproterozoics of NW Indian shield. 相似文献
Yudai is a newly discovered copper deposit associated with a porphyritic quartz diorite, in the Kalatag district of the eastern Tianshan, China. SHRIMP U-Pb dating of zircons from the diorite yielded an age of 432 ± 3 Ma. The diorite is peraluminous (ASI = 0.98–1.10), calc-alkaline to tholeiitic with high Al2O3 of 16.6–17.7 wt% and Mg# of 57.4–67.4. Trace element characteristics of the diorite show it is enriched in Ba, K and Sr, and depleted in Nb, Ta, Ti, with a positive Eu anomaly and high Sr/Y and La/Yb ratios. This diorite has positive εNd(t) values ranging from 6.2 to 8.4 with low initial 87Sr/86Sr ratios of 0.704336 to 0.704450. These geochemical and isotopic characteristics indicate that the adakite-like diorite, associated with the copper mineralization, was emplaced in an island arc setting and resulted from partial melting of subducted oceanic plate in a mantle wedge. 相似文献