本文選題：大陸槽礦床 + 碳酸巖-正長巖雜巖體　； 參考：《巖石學(xué)報(bào)》2017年07期

【摘要】：冕寧-德昌稀土(REE)礦帶位于青藏高原東部,受川西一系列走滑斷裂控制,大陸槽礦床是礦帶中唯一位于南部的大型REE礦床。在前人研究基礎(chǔ)上,結(jié)合近年來對整個稀土礦帶地質(zhì)填圖和室內(nèi)研究,重點(diǎn)對大陸槽礦床的成礦特征、賦礦圍巖及其蝕變、礦石類型、成礦流體來源和流體包裹體演化等方面與同一礦帶內(nèi)的其它礦床進(jìn)行了詳細(xì)對比,進(jìn)一步總結(jié)了碳酸巖型(含碳酸巖-正長巖雜巖體)REE礦床的成礦過程。大陸槽礦床的No.1號和No.3號礦體均位于碳酸巖-正長巖雜巖體內(nèi),分別由不同隱爆角礫巖筒所控制。以往研究認(rèn)為兩個礦體的碳酸巖-正長巖雜巖體侵位的年齡都在12Ma左右,本次研究發(fā)現(xiàn)在26.49±0.63Ma已經(jīng)存在碳酸巖-正長巖雜巖體巖漿活動。大陸槽REE礦床受隱爆角礫巖構(gòu)造活動和風(fēng)化作用的影響,礦石類型以角礫巖型和風(fēng)化型為主,脈石礦物和礦石礦物在手標(biāo)本尺度和鏡下很難辨認(rèn)。通過野外觀察、鏡下礦物共生組合、包裹體顯微測溫等研究發(fā)現(xiàn),大陸槽礦化過程和牦牛坪礦床相似,只是礦化規(guī)模較小,礦化階段分為巖漿巖階段-偉晶巖階段(600℃)-高溫?zé)嵋弘A段(450~350℃)-低溫?zé)嵋弘A段(350℃),氟碳鈰礦形成于熱液階段的晚期。根據(jù)偉晶巖階段至熱液階段氟碳鈰礦中流體包裹體的特征,發(fā)現(xiàn)多期次隱爆角礫活動導(dǎo)致大氣降水和碳酸巖中脫出的CO_2的加入,使得成礦流體的密度(0.732~0.631g/cm~3)、壓力(2436~101bar)逐漸降低,直至成礦。此外,巖相學(xué)觀察和拉曼測試分析也表明包裹體從熔融包裹體過渡到含重晶石、螢石、天青石子晶的富CO_2包裹體、氣液兩相包裹體,顯示了成礦流體由巖漿至熱液的轉(zhuǎn)化過程。大陸槽礦床中的包裹體陰離子以SO_4~(2-)為主,氣體以CO_2為主,成礦流體中陽離子主要為K~+、Na~+、Ca~(2+)、Sr~(2+)、Ba~(2+)和稀土元素陽離子,表明流體屬于SO_4~(2-)-CO_2-H_2O體系,與礦帶中其它礦床的成礦流體體系一致。成礦流體的主要成分是巖漿水、大氣水和碳酸巖脫碳作用形成的CO_2,后者導(dǎo)致熱液方解石和氟碳鈰礦的O同位素(氟碳鈰礦和方解石:δ~(18)O=5.8‰~12.5‰)值升高。已有研究顯示礦帶中不同礦床的脈石礦物如重晶石、天青石的Sr-Nd-Pb同位素與碳酸巖-正長巖雜巖體的相關(guān)數(shù)值基本一致,表明這些脈石礦物來源于碳酸巖-正長巖雜巖體。多期次隱爆角礫巖化作用及大陸槽斷裂相關(guān)的構(gòu)造活動促進(jìn)了成礦流體的循環(huán),直接或間接導(dǎo)致了大陸槽隱爆角礫巖型和風(fēng)化型礦石的形成。盡管在大陸槽和牦牛坪礦床可以識別出表生氧化階段,但這一過程并不伴隨稀土礦化,熱液階段才是稀土沉淀的主要階段。研究還強(qiáng)調(diào)了碳酸巖發(fā)育的大陸槽No.3礦體和里莊礦床主要出現(xiàn)的霓長巖化與礦化無關(guān),而牦牛坪礦床地表并無霓長巖化蝕變。在以往和本次研究的基礎(chǔ)上,建立了川西碳酸巖-正長巖型稀土礦床的成礦模式。
[Abstract]:The Mianning Dechang REE) ore belt is located in the eastern part of the Qinghai-Tibet Plateau and controlled by a series of strike-slip faults in western Sichuan. The continental trough deposit is the only large REE deposit in the southern part of the ore belt. On the basis of previous studies, combined with geological mapping and laboratory study of the whole rare earth ore belt in recent years, the metallogenic characteristics of continental trough deposits, ore-bearing surrounding rocks and their alteration, ore types are emphasized. The source of ore-forming fluid and the evolution of fluid inclusions are compared in detail with other deposits in the same ore belt, and the metallogenic process of carbonatite type (carbonatite-syenite complex) ore deposit is summarized. The No.1 and No.3 ore bodies of continental trough deposit are both located in carbonatite syenite complex and controlled by different crypto-explosive breccia tubes respectively. Previous studies have shown that the emplacement age of the carbonate syenite complex in the two orebodies is about 12Ma. The magmatic activity of the carbonatite syenite complex has been found in 26.49 鹵0.63Ma. The REE deposit in continental trough is affected by the tectonic activity and weathering of cryptoexplosive breccia. The ore types are mainly breccia type and weathering type. The gangue minerals and ore minerals are difficult to identify on hand scale and under microscope. Through field observation, mineral symbiotic assemblage under microscope and microthermometry of inclusions, it is found that the mineralization process of continental trough is similar to that of yak Niuping deposit, but the mineralization scale is relatively small. The mineralization stage is divided into magmatic rock stage, pegmatite stage, 600 鈩，

本文編號：1873125