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Geological Characteristics And Metallogenesis In Habo Porphyry Cu-Mo-Au Deposit, Yunnan, China

Posted on:2011-10-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:X P ZhuFull Text:PDF
GTID:1100360302992523Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
Habo porphyry Cu (-Mo-Au) deposit is located in the southwest of the Ailaoshan-Red River Cenozoic metallogenic belt. The Habo intrusive complex is divided into the Pingshan Granite, the Sandaoban Granite, the Ashu Granite and the Habo South Granite. Following emplacement of these granites bodies, four stages of porphyries, ie. biotie-quartz monznite porphyry, quartz-monzonite porphyry,monzonite porphyry and later diorite porphyry occurring as pipes, were intruded into Habo South Granite. Intense feldspathic alteration and biotitic alteration associated by quartz storckwork occur in the Habo deposit alteration center, which is surrounded and overprinted by later feldspar destructive alteration. Cu-Au mineralization mainly occurs as quartz-chalcopyrite veinlets in the outer part of potassic alteration zone, and Mo mineralization occurring mainly as quartz-molybdenite veinlets, is mixed with Cu-Au mineralization but a little far away to the alteration center. The molybdenum mineralization age at Habo is 35.47±0.16Ma, determined by the Re-Os method by LA-ICPMS.Geochemically, the Habo South Granite and four stages of porphyries are all enriched in potassium, enriched in large-ion lithophile elements (eg. K, Rb, Sr, Ba,Th, La) and light rare earth elements, depleted in high field-strength elements and heavy rare earth elements, with relative hagh (87Sr/86Sr)t (0.70665~0.70831) and negativeεNd(t)( -5.3 ~ -2.5),similar to ore-bearing porphyries in Jianshajiang– Ailaoshan alkaline-rich porphyries belt in Eastern Tibet. Zircons selected from Habo South granite, biotite-quartz-monzonite porphyry and quartz-monzonite porphyry were analysed using the LA-ICPMS U-Pb method and gave ages at 35.37±0.48 Ma, 36.20±0.20 Ma and 36.19±0.22 Ma respectively. The similar mineralization age and rock-forming ages suggest that the magmatism and mineralization was a continuous process, and similar to the process at the Yulong porphyry copper deposit.Several stages of veinlets can be observed, and the evolution sequence of vein types is magnetite-quartz veinlets→early quartz veinlets→quartz-chalcopyrite veinlets→quartz-molybdenite veinlets→quartz-sericite-pyrite veinlets→pyrite-chalcopyrite veinlets. Early quartz, quartz-chalcopyrite and quartz-molybdenite veinlets were selected to perform fluid inclusions research. The Cathodoluminescence images of early quartz, quartz-chalcopyrite and quartz-molybdenite veinlets indicate that all were overprinted by later hydrothermal fluids. Vapor inclusions, vapor-rich inclusions, liquid-rich inclusions, and brine inclusions were found in all three types of veinlets, and CO2-bearing inclusions were found locally. Using Laser Raman analysis, we found that CO2 and SO2 are very abundant in all these inclusions. The coexistence of these several types of fluid inclusions with similar homogenization temperature ranges, and some brine inclusions homogenizing by the simultaneous disappearance of vapor and halite, indicate that all these fluids recorded by these three types of veins experienced"secondary boiling".Vapor-rich and brine inclusions are abundant in early quartz veins, and their homogenization temperatures are similar, which shows that in the Habo deposit the silicate melt directly exsolved two coexisting fluid phases, a vapor and a hypersaline liquid, and the hypersaline fluid is the main carrier of metals. When the fluids migrated upward, at the temperature of ~400°C, the hypersaline liquid entered the two-phase separation field, causing intense boiling and phase separation. With the vapor fluids escaping, the solubility of Cu-Au in the hypersaline fluid decreased, accompanied by intense Cu-Au mineralization. Mo was partitioned into hypersaline fluid during the whole fluid evolution and enriched gradually. On progressive cooling and boiling, the solubility of both Mo and silicates decrease, which is accounted for Mo saturation and deposition.The ore-forming mechanism in Habo should be as the following. Alkaline-rich magma which generated from lower crust intruded along Oumei faults, and formed biotite-quartz-monzontie porphyry, quartz- monzonite porphyry, monzonite porphyry and the later diorite porphyrite. During the intruding and crystallizing process, hydrothermal fluid that exsolved from alkaline-rich magma by"first boiling", mixed with fluid generated from magma chamber, and comprised the initial metal-bearing fluid in Habo porphyry deposit. On cooling and uplifting, the initial fluid kept on experiencing"secondary boiling", and reacted with these host rocks, producing K-feldspathic alterantion, biotitic alteration, chloritic alteration and phyllic alteration, associated by Cu-Au mineralization and Mo mineralization.
Keywords/Search Tags:Habo, Porphyry copper deposit, Alkaline-rich porphyry, Fluid evolution, Ore deposit genesis
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