岩石学报
巖石學報
암석학보
ACTA PETROLOGICA SINICA
2004年
4期
773-790
,共18页
菱镁矿%滑石%白云石%流体包裹体%流体包裹体的化学地质温度计%P-T条件%蒸发途径%Gemericum%喀尔巴阡山脉西部
蔆鎂礦%滑石%白雲石%流體包裹體%流體包裹體的化學地質溫度計%P-T條件%蒸髮途徑%Gemericum%喀爾巴阡山脈西部
릉미광%활석%백운석%류체포과체%류체포과체적화학지질온도계%P-T조건%증발도경%Gemericum%객이파천산맥서부
Magnesite%Talc%Dolomite%Fluid inclusion%Fluid inclusions chemistry geothermometry%P-T conditions%Evaporation trend%Gemericum%Western Carpathians
Gemerska Poloma矿床是个重要的滑石矿床(储量20万吨),位于西喀尔巴阡山脉Germeric地区.部分滑石化的镁质碳酸盐体赋存在早古生代火山沉积杂岩体中(黑色片岩,变质泥岩),在Variscan变质作用(M1)过程中受到了绿泥石-黑云母带区域变质相的改造.这种原岩是石灰岩的矿体由白色-灰白或者灰色-黑色的菱镁矿与白云石1组成,被次生的白云石2和滑石脉切割.本次研究考察了两次变质事件(M1和M2)的几个连续的矿物组合,最早的组合包括铁白云石,镁菱铁矿与菱铁矿,(并与黑电气石,铁绿泥石,磷灰石,与伊利石-白云母伴生),它们以微小残留物形式产出在菱镁矿和白云石1中,其形成可能早于M1变质作用高峰期.M1变质事件的高峰期以富铁金云母,镁绿泥石1,镁电气石(黑电气石的边缘)和石英的组合为代表.在M1退变质作用过程中,发生了镁交代作用,开始是白云石1结晶,接下来形成菱镁矿,最后是以铁菱镁矿沿裂隙的形成而终.根据碳酸盐地质测温原理,M1变质事件的高峰期温度为460～490°C,变质矿物组合特征也支持这一测温结果.滑石,白云石2,与镁绿泥石2沿着镁碳酸盐岩石裂隙的发育,主要受到M2变质事件的影响,这个变质事件与较年青的Alpine造山事件有关.菱镁矿流体包裹体的研究表明,成矿流体具有复杂的组成,可能以MgCl2组分为主,主要来源于蒸发卤水的演化.原生流体包裹体的盐度～35(wt%MgCl2),均一温度变化范围是216～235℃.石英中流体包裹体也显示了以MgCl2组分为主的相似流体组成,但均一温度比较高,为248～313℃.如果假定石英与M1变质事件同期,那么由流体包裹体计算出的M1变质峰期压力范围是250～350MPa(9～13km),因此地温梯度是35～40℃/km.假定这个梯度在镁交代成矿过程中保持不变,那么相关流体在180～280MPa(7～11km)的压力下的温度为300～350℃.流体包裹体的淋滤分析表明,流体中Cl/Br与Na/Br都很高,说明流体具有蒸发特征.而在Gemeric地区只有在晚二叠纪到早三叠纪这段时间才有如此大量的卤水形成.因此,二叠纪的伸展构造运动与形成菱镁矿的热液系统的形成有关.
Gemerska Poloma礦床是箇重要的滑石礦床(儲量20萬噸),位于西喀爾巴阡山脈Germeric地區.部分滑石化的鎂質碳痠鹽體賦存在早古生代火山沉積雜巖體中(黑色片巖,變質泥巖),在Variscan變質作用(M1)過程中受到瞭綠泥石-黑雲母帶區域變質相的改造.這種原巖是石灰巖的礦體由白色-灰白或者灰色-黑色的蔆鎂礦與白雲石1組成,被次生的白雲石2和滑石脈切割.本次研究攷察瞭兩次變質事件(M1和M2)的幾箇連續的礦物組閤,最早的組閤包括鐵白雲石,鎂蔆鐵礦與蔆鐵礦,(併與黑電氣石,鐵綠泥石,燐灰石,與伊利石-白雲母伴生),它們以微小殘留物形式產齣在蔆鎂礦和白雲石1中,其形成可能早于M1變質作用高峰期.M1變質事件的高峰期以富鐵金雲母,鎂綠泥石1,鎂電氣石(黑電氣石的邊緣)和石英的組閤為代錶.在M1退變質作用過程中,髮生瞭鎂交代作用,開始是白雲石1結晶,接下來形成蔆鎂礦,最後是以鐵蔆鎂礦沿裂隙的形成而終.根據碳痠鹽地質測溫原理,M1變質事件的高峰期溫度為460～490°C,變質礦物組閤特徵也支持這一測溫結果.滑石,白雲石2,與鎂綠泥石2沿著鎂碳痠鹽巖石裂隙的髮育,主要受到M2變質事件的影響,這箇變質事件與較年青的Alpine造山事件有關.蔆鎂礦流體包裹體的研究錶明,成礦流體具有複雜的組成,可能以MgCl2組分為主,主要來源于蒸髮滷水的縯化.原生流體包裹體的鹽度～35(wt%MgCl2),均一溫度變化範圍是216～235℃.石英中流體包裹體也顯示瞭以MgCl2組分為主的相似流體組成,但均一溫度比較高,為248～313℃.如果假定石英與M1變質事件同期,那麽由流體包裹體計算齣的M1變質峰期壓力範圍是250～350MPa(9～13km),因此地溫梯度是35～40℃/km.假定這箇梯度在鎂交代成礦過程中保持不變,那麽相關流體在180～280MPa(7～11km)的壓力下的溫度為300～350℃.流體包裹體的淋濾分析錶明,流體中Cl/Br與Na/Br都很高,說明流體具有蒸髮特徵.而在Gemeric地區隻有在晚二疊紀到早三疊紀這段時間纔有如此大量的滷水形成.因此,二疊紀的伸展構造運動與形成蔆鎂礦的熱液繫統的形成有關.
Gemerska Poloma광상시개중요적활석광상(저량20만둔),위우서객이파천산맥Germeric지구.부분활석화적미질탄산염체부존재조고생대화산침적잡암체중(흑색편암,변질니암),재Variscan변질작용(M1)과정중수도료록니석-흑운모대구역변질상적개조.저충원암시석회암적광체유백색-회백혹자회색-흑색적릉미광여백운석1조성,피차생적백운석2화활석맥절할.본차연구고찰료량차변질사건(M1화M2)적궤개련속적광물조합,최조적조합포괄철백운석,미릉철광여릉철광,(병여흑전기석,철록니석,린회석,여이리석-백운모반생),타문이미소잔류물형식산출재릉미광화백운석1중,기형성가능조우M1변질작용고봉기.M1변질사건적고봉기이부철금운모,미록니석1,미전기석(흑전기석적변연)화석영적조합위대표.재M1퇴변질작용과정중,발생료미교대작용,개시시백운석1결정,접하래형성릉미광,최후시이철릉미광연렬극적형성이종.근거탄산염지질측온원리,M1변질사건적고봉기온도위460～490°C,변질광물조합특정야지지저일측온결과.활석,백운석2,여미록니석2연착미탄산염암석렬극적발육,주요수도M2변질사건적영향,저개변질사건여교년청적Alpine조산사건유관.릉미광류체포과체적연구표명,성광류체구유복잡적조성,가능이MgCl2조분위주,주요래원우증발서수적연화.원생류체포과체적염도～35(wt%MgCl2),균일온도변화범위시216～235℃.석영중류체포과체야현시료이MgCl2조분위주적상사류체조성,단균일온도비교고,위248～313℃.여과가정석영여M1변질사건동기,나요유류체포과체계산출적M1변질봉기압력범위시250～350MPa(9～13km),인차지온제도시35～40℃/km.가정저개제도재미교대성광과정중보지불변,나요상관류체재180～280MPa(7～11km)적압력하적온도위300～350℃.류체포과체적림려분석표명,류체중Cl/Br여Na/Br도흔고,설명류체구유증발특정.이재Gemeric지구지유재만이첩기도조삼첩기저단시간재유여차대량적서수형성.인차,이첩기적신전구조운동여형성릉미광적열액계통적형성유관.
Gemerska Poloma deposit is an important talc deposit (20 Mt of talc), located in the Gemeric unit within Western Carpathians. The partly steatizated Mg-carbonatic carbonate body was formed inside Early Paleozoic volcano-sedimentary complexes (black schist, metapelite) , regionally metamorphosed during Variscan metamorphic event (M1) in chlorite-biotite zone. The body,originally limestone, consists of white-grey and/or grey-black coarse-grained magnesite and dolomite 1 that is cut by veins of younger dolomite 2 and talc. Several successive mineral assemblages within two major metamorphic events M1 and M2 have been recognized.Earliest assemblage consists of ankerite, Mg-siderite and siderite (accompanied by schorl, Fe-chlorite, apatite and illite-muscovite) ,occurring as very small relicts in magnesite and dolomite 1 and probably preceding the peak of M1 metamorphism. The peak of the M1 is represented by the assemblage F-rich phlogopite, Mg-chlorite 1, dravite (the rim of schorl) and quartz. During retrograde part of the M1 successive Mg replacement occurred starting with the crystallisation of dolomite 1, followed by magnesite and terminating by formation of Fe-magnesite along cracks. Based on carbonate geothermometry, the peak of M1 occurred at 460 ～490℃, which is supported by metamorphic mineral assemblage. The M2 metamorphism, related to the younger Alpine orogeny, was responsible for the formation of talc, dolomite 2 and Mg-chlorite 2 along the faults in the host Mg carbonate body.Fluid inclusion study in magnesite showed the presence of fluids with very complex composition, probably MgCl2 dominated brines of evolved evaporitic origin. In primary brine inclusions the salinity reached up to ～35 wt% MgCl2 eq. and homogenisation temperature (Th) occurred in the range 216 to 235 ℃. Fluid inclusion in quartz showed also the presence of MgCl2 dominated brines of similar composition, however, with a higher range of Th values (248 to 313℃). If assuming that the host quartz is coeval with the peak of M1, the fluid inclusion data imply the pressure range for the peak of M1 from ～ 250 to 350 MPa (9 ～ 13 km) , which indicates a thermal gradient of about 35 to 40℃/km. Presuming this gradient remained constant also during the Mg-replacement, the related fluids had ～300 to 350℃ under ～ 180 to 280 MPa (7 ～ 11 km).Leachate analyses of fluid inclusions confirm the evaporitic signature of fluids with very high Cl/Br and Na/Br ratios. Large amounts of evaporitic brines in the Gemeric unit had been generated only from Upper Permian to Lower Triassic. Thus, the Permian extensional tectonics can be associated with the generation of the hydrothermal system forming magnesite.
