The Petrological,Chronology And Chemical Characteristics Of Mesozoic Igneous Rocks In Chenfang District The North Wuyi,and Their Relationship With Mineralization

Magmatic activity in the North Wuyi area was frequent and strong,and the intrusions possesse charateristics of multi-phase and multi-strage activity and complex types.Intrusive rocks in Yanshan period are widely distributed,followed by the Caledonian and Indosinan periods.There are rich multi-meral resources and complex and diverse deposit types in the area.Chenfang region located in the north rim of north Wuyi uplift is a very important copper-polymetallic meral forming areas and in which magma activities are strong.Some deposits ware discovered such as Chenfang iron deposit,Liangjia iron-copper deposit,Xiahu lead-zinc deposit.But the degree of studies about magma rocks in the region is low,so that their formation ages,geochemical characteristics and the relation to the mineralization are uncerntain,which need to solved.Though geologic field work and rock slices identification,Granitoids and monzonitic dioritic rocks are the main rock type.Based on comprehensive analysis of Major and trace elements data and related geochemical discrimination diagram,this paper holds that monzonitic dioritic rocks which belong to Mg andesitic rocks are characteristic of TTG rock associations and formed in the subduction environment and derived from the magma which was produced by oceanic crust partial melting interacting with the overlying mantle wedge.The negative abnormality of Eu and HREE anomaly shows there is remnant of plagioclase in source region.The granite in the Chenfang iron mine,Liangjia iron-copper mine and Niubeiji mine possess the characteristic of high SiO2 content,depletion in Eu,rich in LREE,hige Sr/Yb ratio,which belong to highly fractionated I-type granites.The granites in Gexianshang area possess the characteristic of high SiO2 content,higher Eu negative abnormality,low Nb/Ta ratio and low zircon saturation temperatures,which may be formed in arc-arc collision or arc-continent collision where magma derived from continental crust low degree partial melting.The zircon LA-ICP-MS U-Pb dating results shows the weighted average ages of the granties and monzonitic dioritic rocks and they respectively are 241.8 ±2.4 Ma(MSWD=3.4)of Chenfang,240Ma or so of Liangjia,248.7±3.17Ma(MSWD=7.7)of Niubeiji,235.1 ± 1.4Ma(MSWAF=2.6)of Xiahu and 229.7±2.6Ma(MSWD=6.5)of Yanshiling,which belong to Indo-chinese epoch instead of Yanshan Period.In the east of study area,we get the ages of fine-grained adamellite and granite-porphyry of Gexianshan granite complex.They respectively are 162.8 ± 1.2Ma(MSWD=2.4)?153.9± 2.7Ma(MSWD=7.9)which belong to Yanshan Period.Based on the characteristics of Chenfang iron deposit and Xiahu lead-zinc deposit,ore body not controlled by the contact between the Indo-Chinese epoch monzogranite and the carbonatite in Chenfang mine,Xiahu lead and zinc occurred in the bedding fault under the adamellite.It was preliminarily summarized that the Indo-Chinese epoch granites and adamellite have no direct relation with the mineralization and shows more ore-finding potentia in the deep of southeast.