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Peng G.,Central South University | Peng G.,Qinghai Institute of Geological Survey | Gao G.,Central South University
Geotectonica et Metallogenia | Year: 2013

Chinese Altay region is one of the important parts of Altay metallogenic belt of central Asia, and is a well-known mineralization area of non-ferrous metals, rare metals and precious metals. There are more than 100, 000 pegmatite veins in Chinese Altay region, 90% of which occur in more than 30 pegmatite ore fields. In this paper, the Azubai pegmatite ore field in the central Altay, which is around 500 km2 with the centre coordinate of 88°48'E and 47°56'N, is studied. Remote sensing images of ASTER, RapidEye, QuickBird and ENVISAT-ASAR are used to extract prospecting information on pegmatite deposits in the Azubai region. Greisenization and albitization are the main alterations closely associated with mineralization. Based on the spectral characteristics, the method of Feature-orientated Principal Component Selection (FPCS) was used to optimize the ASTER band combination of 1-4-6-7 and 1-4-6-9 to extract greisenization and albitization respectively. ASTER thermal infrared data were used to estimate the surface content of SiO2, K2O and Na2O based on empirical formula, which provide effective technical support for the classification of magmatic rocks and effective basis for mapping and locating of the contact zones of different lithologies. It is the high reflectivity of pegmatite in the spectral range from visible to near infrared that provides the important physical basis for automatic identification and remote sensing interpretation of pegmatite. The pegmatite interpreted from QuickBird image with spatial resolution of 0.61 m was used to validate the automatic extraction of pegmatite from RapidEye image with 5m spatial resolution whose accuracy is about 86%. ASAR image is only used to do some preliminary experiment to identify pegmatite. Due to the lower spatial resolution, the extracted pegmatite from ASAR image was not used for metallogenic prediction. The conjunction parts of geological structures, contact zones of lithologies and superposed parts of pegmatite enrichment zones and alteration anomalies are the important basis for metallogenic prediction. According to above factors derived from remote sensing, four target areas were delineated, which will provide guidance for further prospecting.

Liu Y.C.,Chinese Academy of Geological Sciences | Hou Z.Q.,Chinese Academy of Geological Sciences | Yu Y.S.,Wuhan Institute of Geology and Mineral Resources | Tian S.H.,Chinese Academy of Geological Sciences | And 2 more authors.
Acta Petrologica Sinica | Year: 2013

Changdu region, located in the northeastern margin of Tibetan collisional orogenic belt, is the important part of Southwest 'Sanjiang' metallogenic belt. Carbonate Posted Pb-Zn deposits controlled by thrust nappe structures are abundant and with plenty reserves in this region. Lalongla deposit is located in the southwest of the most famous carbonate-hosted Pb-Zn ore concentration area in Changdu region and is a typical representative. The Pb-Zn mineralization of Lalongla deposit is born in the hanging wall of a thrust fault and ore bodies, mainly produced as lens, distribute along a facies transition between mud shale in Jiapeila Formation and limestone in Bolila Formation in Late Triassic. Breccia and mesh-vein are main ore structures and galena, sphalerite and smithsonite are main ore minerals. The ore-control factor and ore occurrence in this deposit represent a new carbonate-hosted deposit type in 'Sanjiang' metallogenic belt and then it is named as Lalongla type. The main ore-forming process in this deposit can be divided into Period I (shortened form of sulfide period) and Period II (shortened form of sulfide-carbonate period), between which a compressing deformation occurred. Two kinds of fluid inclusion including LV inclusion rich in liquid and LV inclusion rich in CO2 and CH 4 occur in Period I. A microthermal testing work suggests two kinds of hydrothermal fluids in this period, which are with low temperature (130 ∼140°C), high salinity (23% ∼24% NaCleqv) and middle to high density (1. 10 ∼1. 12g. cm) nature and with middle to low temperature (170∼180t), high salinity (23% ∼24% NaCleqv) and middle to low density (1.06 ∼1. 08g. cm-3) nature, respectively. For the two periods, the liquid parts of hydrothermal fluids both belong to Ca2+-Mg 2+-Na+-K+-SO4 2--CI --F-NO3 system and the ion contents, H-0 isotope composition (-137%o∼-110%o for δDv-SM0W and -2. 92%o ∼13. 42%o for δ18 Ov-SM0W), C-O isotope composition of calcite (0. 9%o ∼7. 2%o for δCv-PDB and 9. 1%o ∼26. 5%o for δ18 Ov-SM0W) are all similar to each other, suggesting two resources, including low-temperature, high salinity basin brine and middle-temperature, high-salinity regional fluid composed by evaporated-concentrated seawater cocooned in strata, metamorphic water released by metamorphic rock and the meteoric water, for the hydrothermal fluids. The sulfur isotope composition for the two Periods is still similar. The S S values of sulfide are negative (-24. 7%o ∼-11. 5%o), of barite are positive (11. 3%o ∼22. 9%o) and of gypsum (2. 0%o ∼4. 7%o) are between the two former, suggesting reducing S comes from biological sulfate reduction which derives from the basinal brine descending from overlying Paleogene basin and evaporated-concentrated seawater cocooned in strata, and mixing of two kinds of fluid, which are local fluid rich in reducing sulfur and regional fluid rich in metal, causes the deposition of mineralized minerals. The Pb isotope composition of galena in the two periods are nearly the same and the ranges of 206 Pb/204 Pb,207 Pb/204 Pb and 208 Pb/204 Pb are 18. 8646 ∼18. 8835, 15. 6619 ∼15. 6677 and 38. 9404 ∼38. 9796, respectively, proving that Pb isotope comes from metamorphic basement and limestone (and clastic rock) caprock distributed in the orogenic belt. By comparing Lalongla deposit with carbonate-hosted deposits in 'Sanjiang' belt, the authors finally point out that Lalongla deposit could be classified as MVT-like deposit controlled by thrust nappe and its moralization model can be explained as followings: Structural trap formes in the carbonate formation due to thrust nappe. The basinal brine in Paleogene basin descends, accumulates, and generates the local fluid reservoir rich in H2S accompanied by the biological sulfate reduction. Regional fluid released by the compression deformation migrates along the main detachment zone of thrust nappe, leachs oreforming minerals in strata and generates allochthonous fluid rich in metallic elements. Along extended faults by final stretch of local thrust faults regional fluid ascends to the interface between limestone and mud shale, the favorable space, mixes with local fluid and leads to the uninstall mineralization of metal materials and the lens ore-bodies along the facies transition between different rocks finally form.

Tian S.H.,Chinese Academy of Geological Sciences | Hou Z.Q.,Chinese Academy of Geological Sciences | Yang Z.S.,Chinese Academy of Geological Sciences | Liu Y.C.,Chinese Academy of Geological Sciences | And 3 more authors.
Acta Petrologica Sinica | Year: 2011

The Mohailaheng and Dongmozhazhua Pb-Zn deposits in the Yushu area of Qinghai Province, located in the northeast margin of Qiangtang terrane which is between Jinshajiang suture zone and Bangonghu-Nujiang suture zone, are the two typical Pb-Zn deposits in the Cu-Pb-Zn polymetallic mineralization belt for the northern part of the Nujiang-Lancangjiang-Jinshajiang area. The authors thought the sources of ore-froming material were derived from the sedimentary strata by the research of sulfur, lead, strontium and neodymium isotope compositions of the Dongmozhazhua lead-zinc ore deposit. On the basis of geological field observations, the authors also made the research on the Mohailaheng lead-zinc ore deposit and selected sulfide minerals and barite for S isotope compositions analyses, sulfide minerals, gangue minerals and regional strata for Pb isotope compositions analyses, and gangue minerals for Sr-Nd isotope compositions. δ34 S values of sulfide minerals are -30.0‰ - +7.4‰, and show peaks at -18‰ - -2‰, reflecting the characteristic of light sulfur. δ34S values of barite are 20.2‰ - +24.2‰, implying the derivation of Tertiary continental facies basin. The ore deposit displays wide variations in sulfide δ34S values, indicating multiple sulfur sources. On account of the lack of magmatic activity, it is realistic to view the rocks in the basin as the source of sulfur. Sulfur in the rocks was transferred into hydrothermal fluids via fluid-rock interaction. Therefore, the variation in rock types across the basin is likely to influence the variation of sulfur isotopic compositions. Reduced sulfurs were mainly derived from the biogenic sulfate reduction or the thermochemical reduction of sulfur-bearing organic matter, implying that sulfur came from the sedimentary basin. The 206Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb ratios for sulfide minerals vary in ranges of 18.298-18.694, 15.298-15.721 and 38.169-38.894, respectively. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for gangue minerals are between 18.418-18.672, 15.418-15.719 and 38.403 38.845, respectively. In the diagrams of 207Pb/204Pb- 206Pb/204Pb and 208Pb/204Pb- 206Pb/204Pb, the Pb isotope compositions of the sulfide minerals and gangue minerals fall into the regional upper crust lead zone, similar to MVT deposit, implying that Pb might have come from the upper crust rocks. The (87Sr/86Sr)i, εSr(t) , (143Nd/144Nd)i and εNd(t) ratios for gangue minerals vary in ranges of 0.70851-0.70906, 57.4-65.2, 0.512265-0.512361 and -6.5 - -4.6, respectively. The Sr-Nd isotope compositions of the gangue minerals indicate that their matter sources also came from the upper crust rocks. On the whole, the characters of sulfur, lead, strontium and neodymium isotope compositions of the Mohailaheng lead-zinc ore deposit in the Yushu area are the same as those of the Dongmozhazhua lead-zinc ore deposit, implying that they both derived from the sedimentary strata. Together with the geological and geochemical features of the Mohailaheng and Dongmozhazhua Pb-Zn deposits, the authors discussed their dynamical settings.

Qi S.S.,China University of Geosciences | Qi S.S.,Qinghai Institute of Geological Survey | Qi S.S.,Qinghai Prov Key Laboratory Of Geol Processes And Mineral Resources Of Northern Qinghai Tibetan Plateau | Song S.G.,Peking University | And 6 more authors.
Acta Petrologica Sinica | Year: 2014

Eclogite and the retrograde amphibolic eclogite, occurred as tectonic lenses, are found in the metamorphic basement, western part of the East Kunlun, based on the results of 1 : 250000 regional geological survey. They are intermittently scattering about 20km along Xiaozaohuo-Suhaitu-Xiarihamu-Laningzaohuo area. Most of the eclogites are retrograded into amphibolic eclogites, they consist of the peak metamorphic mineral assemblage (garnet + omphacite + ilmenite + rutile) and the later stage retrograde mineral assemblage (hornblende (green) + plagioclase). The edge of the garnet grains develops needle-like hornblende and particulate plagioclase symplectic corona texture, forming white eye rims about 0.15 ∼ 1cm in size. The composition of garnet is Alm52-53And4.2Spess0.7-1.2 Gross21.7-22Pyr19-20, Jadeite molecular in omphacite is 30.14mol% ∼ 37.7mol%. Estimation of eclogite-facies metamorphic conditions shows P≈20kbar, T≈660 ∼ 700°C, and the amphibolite facies retrograde metamorphic conditions of P≈7kbar, T≈550°C. The rocks had experienced a retrogressive process of significant cooling and decompression. Most of the CL images of zircons from the eclogites show sector zoning or "fir leaves" structure. Th/U ratio ranges in 0.007 ∼ 0.09. Zircon U-Pb age (LA-ICP-MS) is 411.1 ± 1.9Ma (n=17), which represents the peak metamorphism age of eclogite-facies. Combined with the analysis of regional metamorphic and magmatic events, the peak stage of the high-pressure metamorphism is determined to be Late Silurian-Early Devonian, which is probably associated with a massive continent-continent collision event. The discovery is significant for the tectonic study of the Kunlun orogenic belt.

Chen Y.-S.,China Earthquake Administration | Li S.-P.,Qinghai Institute of Geology and Mine | Li S.-P.,Qinghai Institute of Geological Survey | Li Y.-X.,No 8 Geological Exploration Institute Of Qinghai | And 4 more authors.
Northwestern Geology | Year: 2010

The copper-molybdenum deposit in Narigongma area lies in the Qiangbei-Changdu block, which is in the north of Bangonghu-Nujiang suture zone and the south of Jiangshajiang suture zone. This deposit and Yulong porphyry cupric deposit belong to the same mineral belt. The cupric ore bodies generally distribute in the upper porphyry and melaphyre, and are complicated in shape and simple in mineral type. The molybdenum ore bodies mostly lie in granide, diorite and black mica granide and a few in pyrite propylitization basalt. The fluid inclusion shows that the source of impregnating copper-molybdenum deposit is from lower crust. The composite rupture is mainly factor for controlling the mineral deposit in this area, and the copper-molybdenum deposit lies in the crossed area of large faults. The intermediate intrusive is inner controlling factor, and the fissure tectonic system also plays the important rule for controlling minerlization.

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