东南沿海早白垩世锡(钨)矿床地质特征、成岩成矿背景及找矿勘查启示

Geological characteristics,geodynamic setting of magmatism and metallogeny of Early Cretaceous Sn(W)deposits in southeastern coastal belt of China,and their implication for exploration

我国华南是世界上最重要的锡矿资源省之一,其锡矿成矿时代从新元古代、古生代、早中生代至晚中生代均有发育,其中以晚中生代锡矿成矿作用最为重要,成矿集中在中晚侏罗世(160~150Ma)和晚白垩世(100~80Ma)。然而,最近在东南沿海成矿带新识别出一期早白垩世锡(钨)(145~130Ma)成矿事件,改变了以往华南锡(钨)矿床时空分布格局。本文在详细介绍东南沿海早白垩世锡(钨)矿床地质特征基础上,系统总结了其成岩成矿时空分布,并与南岭板内锡(钨)成矿作用进行对比,浅析了早白垩世锡(钨)矿的成岩成矿背景和找矿潜力。研究显示,早白垩世锡(钨)成矿主要发生在东南沿海成矿带的粤东和赣州会昌地区,矿床类型以斑岩型和锡石硫化物型为主。与成矿有关的岩石为黑云母花岗岩和花岗斑岩,成因上属于高分异I型或A型,与南岭板内锡(钨)矿相比,具有较高的锆石ε_(Hf)(t)值和较低δ~(18)O值,以及较高成岩温度,表明成岩过程中有较多新生地壳或地幔物质加入。结合区内发育同时期基性岩脉,认为华南这期早白垩世锡(钨)矿形成于岩石圈伸展背景,与古太平洋板块俯冲后撤有关。最后指出覆盖大面积晚白垩世火山岩的东南沿海地区,火山岩盖层下部具有寻找该期锡(钨)矿床的找矿潜力。

South China is one of the most important tin provinces in the world,and the tin mineralization formed from Neoproterozoic,Early Paleozoic,to Early and Late Mesozoic are well developed in this area.In particular,the Late Mesozoic tin mineralization is the most important one,happened at two age peaks of the Middle-Late Jurassic(160~150 Ma)and Late Cretaceous(100~80 Ma),respectively.However,an Early-Cretaceous(145~130 Ma)tin(tungsten)metallogenic event has also been newly recognized in southeastern coastal belt of China.This makes a change in temporal-spatial framework of tin(tungsten)deposits.In this paper,based on detailed observations of geological characteristics of the Early Cretaceous tin(tungsten)deposits in southeastern coastal belt,we summarize the temporal-spatial distribution of these deposits and their associated magmatisms,and compared them with those in the Nanling Range,in order to identify their metallogenic geodynamic setting and implications for metallogenic potential.The Early Cretaceous tin(tungsten)deposits are mainly developed in the coastal eastern Guangdong Province and Huichang district of the southern Jiangxi Province.Genetically,the tin mineralization mainly comprises porphyry and cassiterite-sulfide-vein types,and associated granitoids include biotite granite and granitic porphyry characterized by high-fractionated I-and A-type affinities.Compared with those in the Nanling Range,these granites display higher zirconεHf(t)andδ18O values,as well as higher magma temperatures,indicating a contribution of more mantle or juvenile crustal components.Given the coeval mafic dikes in the region,we suggest that the Early Cretaceous tin(tungsten)deposits were formed in the setting of lithospheric extension,triggered by the retreat of the subducting paleo-Pacific plate.Finally,we suggest that there is potential for tin(tungsten)exploration under the large-scale cover of Late Cretaceous volcanic rocks in southeastern coastal belt of China.