CAO Hua-wen ¹, ZHANG Shou-ting¹, WU Jun-de², LIN Jin-zhan¹, ZHANG Wei¹, CHEN Hui-jun¹, ZHANG Yun-hui¹

（1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;
2. Group Company of Stannary Gejiu in Yunnan, Gejiu 661000, China）

Abstract: Hydrothermal copper-tin polymetallic deposits are distributed in altered basalt stratum mainly in Laochang and the west of Kafang in the Gejiu area, Yunnan Province, China. ⁴⁰Ar-³⁹Ar isotopic dating was used to study the age of K-feldspar in Laoka granite and phlogopite in the “basalt-type” copper deposit in the Laoka ore field. The result shows that the K-feldspar of the Laoka rock mass has an ⁴⁰Ar-³⁹Ar plateau age of 71.6±0.29 Ma; and that the alteration phlogopite in the Laochang and Kafang “basalt-type” copper deposits have an ⁴⁰Ar-³⁹Ar plateau age of 81.99±0.85 Ma and 82.46±0.85 Ma respectively, which means that these minerals were formed in the Late Cretaceous. Combined with regional data, this article further indicates that the copper-tin polymetallic ore field in Gejiu has undergone a long magma-hydrothermal evolution and that “basalt-type” copper polymetallic deposits are the products of asthenospheric upwelling and massive lithospheric extension, associated with the magmatic activity in the Late Yanshanian period.

Key words: Laoka; Gejiu; ⁴⁰Ar-³⁹Ar isotopic age; K-feldspar; phlogopite; “basalt-type” copper deposit

ACTA MINERALOGICA SINICA Vol. 34, No. 3, 2014, Page 312-320