滇东地区裂谷盆地内火山—侵入岩序列与金属成矿

碱性岩浆对金属成矿和金属矿集区有独特控制作用,因火山—侵入岩序列与金属成矿和岩浆叠加侵入构造系统识别难度大,长期制约了深部勘探和找矿预测。本文以云南东川铁铜金矿集区(元古宙陆缘裂谷盆地)和个旧锡铜钨铯铷多金属矿集区(三叠纪弧后裂谷盆地)为主,采用大比例尺构造岩相学填图新方法,解析研究了碱性岩浆活动有关的火山—侵入岩侵入序列与岩石组合、裂谷盆地演化和岩浆叠加侵入构造系统,揭示了它们与滇东地区铁氧化物铜金型(IOCG)、铜钴- 金红石- 稀土和锡铜钨铯铷多金属矿叠加成矿内在关系。研究认为：① 云南东川铁铜金矿集区内,新太古代末期碱性岩类以方解石钠长岩(2520±14 Ma)和碱性铁质苦橄岩(2529±77 Ma)为主。新太古界—古元古界小溜口岩组(＞2. 50 Ga)顶部古岩溶风化壳,受中元古代火山喷发—岩浆侵入构造叠加再造形成了特殊单元(独立填图单元, 2. 50~1. 80 Ga),它们是铜钴- 金红石- 稀土矿床的新找矿层位。② 在中元古界因民组一段内,铁钠质碱性基性岩、铁钾质粗面岩和铁质碱性辉绿辉长岩等岩石组合形成于因民期火山断陷成盆期。因民组二段和三段是稀矿山式铁铜矿床储矿层位,铁铜矿层下盘铁钾质粗面岩为独居石型稀土成矿层位。在格林威尔造山期碱性钛铁质辉长岩(1097~1047 Ma)- 碱性钛铁质闪长岩- 碱性二长斑岩等碱性钛铁质侵入岩体,形成了白锡腊深部IOCG矿床和金红石富集成矿。③ 在个旧三叠纪弧后裂谷盆地内,三叠纪碱性苦橄岩和碱玄岩中形成了Sn- Cu- Zn- Li- Rb- Cs初始富集;在晚白垩世浅色花岗岩叠加成矿作用下,形成了金云母矽卡岩型锡铜钨铯铷矿床。④ 裂谷盆地内早期碱性岩中初始富集金属与后期富含成矿金属的碱性侵入岩叠加成矿可能是金属超常富集机理。在东川地区岩浆叠加侵入构造内,岩浆热液角砾岩筒对铜钴- 金红石- 稀土元素叠加富集成矿控制显著;在个旧地区,浅色花岗岩侵入于碱性苦橄岩- 碱玄岩中,对金云母矽卡岩型锡铜钨钴铯铷矿床的叠加富集成矿控制显著。

The volcanic- intrusive rock sequences and metal mineralizations in rifted basin in the eastern Yunnan Province, China

Alkali magmatism exerts a distinctive influence on mineralization processes in metal ore- concentrated areas. However, deep exploration and mineral prediction in the study area face challenges due to the complex interplay of volcanic- intrusive rock sequences, metal mineralization, and superimposing magmatic- tectonic systems. This study focuses on two key regions in eastern Yunnan, China: the Dongchuan Fe- Cu- Au ore concentrated area (Proterozoic marginal rifted basin) and the Gejiu Sn- Cu- W- Cs- Rb polymetal ore concentrated area (Triassic back- arc rifted basin). By applying innovative tectonic lithofacies mapping techniques, we investigated the volcanic- intrusive rock sequences related to alkali magmatic activity, rifted basin evolution, rock associations, and superimposed magmatic- intrusive systems. This approach aims to elucidate the superimposed mineralization of IOCG, Cu- Co- rutile, and Sn- Cu- W- Cs- Rb polymetallic deposits in the region. Our investigation has yielded several noteworthy findings. Firstly, Neoarchean alkali rocks in the Dongchuan Fe- Cu- Au ore- concentrated area are composed of calcite albitite (2520±14 Ma) and Fe- rich alkalipicrite (2529±77 Ma). The Neoarchean- Paleoproterozoic Xiaoliukou Formation Complex (＞2. 50 Ga), particularly its upper part exhibiting homotopy in different lithofacies (2. 50 to 1. 80 Ga), serves as the new host strata for Cu- Co- rutile- REE mineralizations. These strata have been reworked by Mesoproterozoic volcanic- intrusive rocks in the Dongchuan Fe- Cu- Au ore- concentrated area. Secondly, during the Mesoproterozoic stage of volcanic rifting basins, alkaline rocks, including Fe- Na- rich alkali basic rocks, Fe- K- rich trachyte, and Fe- rich alkali diabase- gabbros, formed as part of the first member of the Yinmin Formation. Xikuangshan- type Fe- Cu deposits, or IOCG deposits, are hosted in the second to third members of the Mesoproterozoic Yinmin Formation. Additionally, Fe- K- rich trachyte in the footwall of the Fe- Cu orebody hosts monazite- type REE mineralization. The IOCG system and rutile superimposing mineralization are formed in alkaline Ti- Fe- rich gabbros (1097 to 1047 Ma), alkaline Ti- Fe- rich diorites, and alkaline monzoporphyry, all of which formed during the Greenville Orogeny in eastern Yunnan. Thirdly, Triassic alkalipicrite and tephrite, with primary enrichment of Sn- Cu- Zn- Li- Rb- Cs, were produced in the Triassic arc- back rifted basin in the Gejiu area of eastern Yunnan Province, China. These rocks were subsequently superimposed by leucogranite intrusion, which played a pivotal role in the formation of Sn- Cu- W- Cs- Rb- bearing phlogopite- type skarn. Finally, alkali rocks with initial metal enrichment in the early stage of the rifted basin evolution were superimposed by later- stage alkaline intrusive rocks with metal mineralization. This process represents the primary mechanism for metal mineralization in the rifted basin in eastern Yunnan. Breccia- pipes formed by magmatic hydrothermal fluids in the alkaline magmatic- intrusive tectonic system control the hypernormal enrichment of Cu- Co- rutile- REE mineralization. Conversely,leucogranite intruded into alkalipicrite and tephrite with Sn- Cu- W- Cs- Rb primary enrichment is responsible for the hypernormal enrichment of Sn- Cu- W- Cs- Rb- bearing phlogopite- type skarn.