Characteristics of chlorite minerals from Xiaolonghe tin deposit in West Yunnan,China and their geological implications

Chloritization is obvious near the Xiaolonghe tin deposit.It is closely related to the tin mineralization.Mineragraphy study shows that the chloritization there can be divided into two types, that is,weak chloritization and strong chloritization.The relative parameters of chlorite such as Al IV, Al VI,Fe2+/(Mg2++Fe2+),Mg2+/(Mg2++Fe2+),forming temperature,oxygen fugacity and sulfur fugacity are calculated based on the electron microprobe data.The results show that the contents of Mg and Si increase and the contents of Al,Mn,Fe decrease with the increase of chloritization degree. The chlorite is mainly composed of chamosite which is rich in Fe,indicating that the chlorite forms in a reduced environment.The formation temperature is 196~229℃(averaging 213℃).The lgfO 2 is-43.4~-48.0(averaging-44.6)and the lgfS 2 is-15.9~-18.6(averaging-16.5).The main formation mechanisms are metasomatism-crystallization and migration-crystallization.This indicates that the chlorites are the products at the late stage of tin mineralization and reflects the change of the conditions when the tin deposit forms.