干旱区生态环境知识资源中心

The Yulong porphyry copper ore is the largest one found in collision zone. in the, eastern Tibet, China. The ore-bearing early stage quartz monzonite porphyry and late porphyry, which hosts 6.5 Mt Cu with an outcrop area of 0. 64 km(2) consists mainly of e,. stag stage syenite granite porphyry. The early stage quartz monzonite porphyry has zircon LA-ICP-MS U-Pb age of 41.3 +/- 0.3Ma, with MSWD = 0. 92 and the late stage syenite granite porphyry has zireon LA-ICP-MS U-Pb age of 41.3 +/- 0.3 Ma, with MSWD = 1.24. The zircon age of the Yulong ore-bearing porphyry is indistinguishable within error from an Ar-Ar plateau age 41.7 +/- 0.8Ma and isochron age of 41.3 +/- 0.8Ma for biotite from the potassic alteration zone arid the reported Re-Os age for molybdenite mineralization (40.1 +/- 0.8Ma) of the Yulong deposit. The concordance of the zircon U-Pb data of the early stage monzonite porphyry and the late stage syenite granite porphyry suggests that the Yulong porphyry emplaced essentially the same time. The agreement among zircon U-Pb, molybdenite Re-Os, and the biotite (40)Ar-(39)Ar ages in the Yulong porphyry indicates the Yulong ore-forming system cooled from about 800 degrees C (zircon crystallization temperature) through 500 degrees C (closure temperature for Re-Os in molybdenite) to below 300 degrees C (the closure temperature for Ar in biotite) io a very short period. The duration of the Yulong giant ore-forming system is less that 1Ma.