摘要
花岗斑岩侵入玄武岩中形成相应的铜钼矿化是三江成矿带的特色之一,三江南段的澜沧老厂多金属矿床的花岗斑岩隐伏侵入石炭系玄武质火山岩中,花岗斑岩-玄武岩热液蚀变体系得以完整保存。在确立初始岩石端元的基础上,对花岗斑岩顶盖相的去钠化蚀变及玄武质围岩夕卡岩化过程的元素地球化学进行了初步研究,主要结论包括：（1）花岗斑岩驱动的热液体系以富含Na-Ca-Si-Mn为特征,Na-Ca-Si主要来自花岗斑岩中的斜长石分解蚀变,在花岗斑岩顶盖相中形成极度的Na亏损和极高的K_2O/Na_2O比值（去钠化蚀变）;Si在花岗斑岩顶盖相中弱富集,Si-Ca在玄武质围岩夕卡岩化过程中明显富集（w（Si O_2）平均增加了4%~5%,w（Ca O）平均增加了5%左右）,目前在蚀变体系中没有发现Na的明显富集,推测Na可能被热液搬运进入地表径流系统;Mn是特征蚀变元素,可能来自深部花岗斑岩,在花岗斑岩顶盖相及玄武质围岩中都得到明显富集（平均富集0.4~1.2倍）。（2）矿化元素中Mo主要来自花岗斑岩,在斑岩顶部及玄武质围岩中富集,局部成矿;Sn-Zn主要来自花岗斑岩,但目前没有在花岗斑岩内外接触带发现矿化;Ag-Pb-Bi的主要物源是玄武岩,在斑岩顶部富集,在更远端的碳酸盐岩地层中成矿;Cu也主要来自玄武岩,在玄武岩夕卡岩化过程中局部成矿。（3）稀土元素在花岗斑岩的蚀变过程主要表现为活化迁移亏损,在活化过程中Eu发生了比较明显的分异（δEu 0.85~1.32）;玄武岩夕卡岩化过程中,热液流体携带的稀土元素在橄榄玄武岩中基本收支平衡,但在拉斑玄武岩中明显富集,并以显示弱的正Eu异常为特征。
Cu-Mo mineralization caused by granitic porphyry invading into basalt formation is one of distinctive metallogenesis located in Sanjiang metallogenic belt. The hydrothermal alternation system has been completely preserved in Laochang polymetallic deposit（Lancang Area, Yunnan Province, the southern end of Sanjiang belt, China）, in which Carboniferous basaltic rocks have been invaded by deep concealed granitic porphyry. Based on determining the initial end-member rocks, element geochemistry research has been focused on desodiuming alteration in upper part of granitic porphyry and skarnization in basaltic wall rocks. Some results have been concluded.（1） The hydrothermal fluid in the upper part of granitic porphyry is enriched with Na-Ca-Si-Mn which is mostly from plagioclase decomposited alteration, characterized with extremely depleted Na and high K_2O/Na_2 O rate（Desoudiuming）. Till now no Na-enriched alteration has been found, we speculated that the element Na should be transferred into the runoff system. There is about 1%-2% Si O_2 enriched in the upper part of granitic porphyry, however, there are obviously enriched Si and Ca in basaltic wall rock during skarnization（Si O_2 average increment is about 4% to 5% and Ca O average increment is about 5%）.The characteristic Mn sourced from deep granite has most enriched 0.4-1.2 times in the upper part of granitic porphyry and basaltic wall rocks.（2） Elements Mo-Sn-Zn are mainly from granitic porphyry. Mo is enriched in the upper part of porphyry and adjacent basaltic wall rocks and extensively low ore-grade Mo mineralization has been confirmed, however, no Sn-Zn mineralization in contact zone of granitic porphyry has been found at present. Elements Ag-Pb-Bi-Cu mainly come from basalt. Cu is enriched in basaltic wall rocks and locally low ore-grade mineralization has been proved. Ag-Pb-Bi are enriched in the upper part of granitic porphyry and Ag-Bi-enriched galena veins have been explored in carbonate formation overlain upon Carboniferous basalt.�
出处
《矿物学报》
CAS
CSCD
北大核心
2016年第3期329-342,共14页
Acta Mineralogica Sinica
基金
国家自然科学基金项目(批准号:41072054
41530210)
国家973项目(编号:2015CB452603)
关键词
花岗斑岩
去钠化蚀变
玄武岩夕卡岩化
喜山期花岗斑岩
澜沧老厂
hydrothermal alteration system
desodiuming alteration
basalt skarnization
Himalayan granitic porphyry
Laochang
Lancang
Yunnan
