岩石学报
巖石學報
암석학보
ACTA PETROLOGICA SINICA
2004年
4期
855-876
,共22页
菱镁矿%包裹体%包裹体流体化学%蒸发趋势%地质温度计%P-T条件%C-O-Sr同位素%Gemericum区%西喀尔巴阡山
蔆鎂礦%包裹體%包裹體流體化學%蒸髮趨勢%地質溫度計%P-T條件%C-O-Sr同位素%Gemericum區%西喀爾巴阡山
릉미광%포과체%포과체류체화학%증발추세%지질온도계%P-T조건%C-O-Sr동위소%Gemericum구%서객이파천산
magnesite%fluid inclusion%fluid inclusion chemistry%evaporation trend%geothermometry%P-T conditions%C-O-Sr isotopes%Gemericum%Western Carpathians
Kosice矿床是斯洛伐克第二大的菱镁矿床(150Mt),位于Gemeric的东部.其镁质碳酸盐矿体赋存于石炭纪石灰石和含白云石的石灰石中,同时下盘黑色片岩中也含有被铁质碳酸盐交代的薄层碳酸盐透镜体.在华力西期造山运动(M1)中,古生代岩石受到了低级变质作用(绿泥石带).镁交代作用始于白云岩1的结晶作用,其后形成菱镁矿,最终沿裂隙形成铁菱镁矿.铁质碳酸盐包括早期铁白云石-白云石,铁白云石和后期含方解石和石英的菱铁矿.根据碳酸盐矿物对地质温度计,白云石l结晶作用发生在300～340℃.这一结果与M1的变质矿物组合(绿泥石,白云母-伊利石)吻合.铁白云石的结晶作用发生在320～370℃.少量细脉中可见白云石2,绿泥石和伊利石-多硅白云母,它们是由于阿尔卑斯期造山运动M2变质作用形成的更晚的矿物组合.菱镁矿的流体包裹体(FI)研究,显示存在不同成分的热卤水,卤水成分变化相当于NaCl含量21～42 wt%,但其它成分的盐含量高于NaCl,溶解的CO2含量也有变化.两相包裹体均一温度(Th)的范围为164～217℃,含石盐子晶包裹体均一温度的范围为217～344℃.富CO2包裹体(盐度相当于NaCl含量1～22wt%,CO2的密度为0.28～0.77 g·cm-3,均一温度为289～344℃)在菱镁矿中是次要的,但这种包裹体在与矿石伴生的石英中是主要的,并且与含石盐子晶流体包裹体共生.在后期镁交代过程中流体中的CO2逐渐增加.和铁质碳酸盐伴生的石英中只有两相包裹体,包裹体中CO2含量有所变化,盐度范围为17～24 wt%的NaCl(或者34～36 wt%的MgCl2),均一温度为152～195℃.包裹体的数据结合碳酸盐地质温度计显示镁交代作用的压力范围是180～320MPa(7～12km),铁交代作用的压力范围是280～420MPa(10～16km),说明地热梯度约为25～35℃/km.包裹体浸出液的分析表明Cl/Br和Na/Br的比值存在变化,但仍旧说明富镁的卤水来源是上二叠纪和下三叠纪的分馏蒸发岩来源.铁质碳酸盐流体的高溴和高碘含量,说明在铁交代过程中周围黑色片岩的明显影响.菱镁矿和铁交代作用,表明交代流体中的碳和二氧化碳,主要是海洋沉积的来源.菱铁矿的"Sr/86Sr比值((0.71124～0.71140),说明锶的多来源,最初应是石炭纪和二叠纪的海水,但它被当地其它陆壳中的锶混染.
Kosice礦床是斯洛伐剋第二大的蔆鎂礦床(150Mt),位于Gemeric的東部.其鎂質碳痠鹽礦體賦存于石炭紀石灰石和含白雲石的石灰石中,同時下盤黑色片巖中也含有被鐵質碳痠鹽交代的薄層碳痠鹽透鏡體.在華力西期造山運動(M1)中,古生代巖石受到瞭低級變質作用(綠泥石帶).鎂交代作用始于白雲巖1的結晶作用,其後形成蔆鎂礦,最終沿裂隙形成鐵蔆鎂礦.鐵質碳痠鹽包括早期鐵白雲石-白雲石,鐵白雲石和後期含方解石和石英的蔆鐵礦.根據碳痠鹽礦物對地質溫度計,白雲石l結晶作用髮生在300～340℃.這一結果與M1的變質礦物組閤(綠泥石,白雲母-伊利石)吻閤.鐵白雲石的結晶作用髮生在320～370℃.少量細脈中可見白雲石2,綠泥石和伊利石-多硅白雲母,它們是由于阿爾卑斯期造山運動M2變質作用形成的更晚的礦物組閤.蔆鎂礦的流體包裹體(FI)研究,顯示存在不同成分的熱滷水,滷水成分變化相噹于NaCl含量21～42 wt%,但其它成分的鹽含量高于NaCl,溶解的CO2含量也有變化.兩相包裹體均一溫度(Th)的範圍為164～217℃,含石鹽子晶包裹體均一溫度的範圍為217～344℃.富CO2包裹體(鹽度相噹于NaCl含量1～22wt%,CO2的密度為0.28～0.77 g·cm-3,均一溫度為289～344℃)在蔆鎂礦中是次要的,但這種包裹體在與礦石伴生的石英中是主要的,併且與含石鹽子晶流體包裹體共生.在後期鎂交代過程中流體中的CO2逐漸增加.和鐵質碳痠鹽伴生的石英中隻有兩相包裹體,包裹體中CO2含量有所變化,鹽度範圍為17～24 wt%的NaCl(或者34～36 wt%的MgCl2),均一溫度為152～195℃.包裹體的數據結閤碳痠鹽地質溫度計顯示鎂交代作用的壓力範圍是180～320MPa(7～12km),鐵交代作用的壓力範圍是280～420MPa(10～16km),說明地熱梯度約為25～35℃/km.包裹體浸齣液的分析錶明Cl/Br和Na/Br的比值存在變化,但仍舊說明富鎂的滷水來源是上二疊紀和下三疊紀的分餾蒸髮巖來源.鐵質碳痠鹽流體的高溴和高碘含量,說明在鐵交代過程中週圍黑色片巖的明顯影響.蔆鎂礦和鐵交代作用,錶明交代流體中的碳和二氧化碳,主要是海洋沉積的來源.蔆鐵礦的"Sr/86Sr比值((0.71124～0.71140),說明鍶的多來源,最初應是石炭紀和二疊紀的海水,但它被噹地其它陸殼中的鍶混染.
Kosice광상시사락벌극제이대적릉미광상(150Mt),위우Gemeric적동부.기미질탄산염광체부존우석탄기석회석화함백운석적석회석중,동시하반흑색편암중야함유피철질탄산염교대적박층탄산염투경체.재화력서기조산운동(M1)중,고생대암석수도료저급변질작용(록니석대).미교대작용시우백운암1적결정작용,기후형성릉미광,최종연렬극형성철릉미광.철질탄산염포괄조기철백운석-백운석,철백운석화후기함방해석화석영적릉철광.근거탄산염광물대지질온도계,백운석l결정작용발생재300～340℃.저일결과여M1적변질광물조합(록니석,백운모-이리석)문합.철백운석적결정작용발생재320～370℃.소량세맥중가견백운석2,록니석화이리석-다규백운모,타문시유우아이비사기조산운동M2변질작용형성적경만적광물조합.릉미광적류체포과체(FI)연구,현시존재불동성분적열서수,서수성분변화상당우NaCl함량21～42 wt%,단기타성분적염함량고우NaCl,용해적CO2함량야유변화.량상포과체균일온도(Th)적범위위164～217℃,함석염자정포과체균일온도적범위위217～344℃.부CO2포과체(염도상당우NaCl함량1～22wt%,CO2적밀도위0.28～0.77 g·cm-3,균일온도위289～344℃)재릉미광중시차요적,단저충포과체재여광석반생적석영중시주요적,병차여함석염자정류체포과체공생.재후기미교대과정중류체중적CO2축점증가.화철질탄산염반생적석영중지유량상포과체,포과체중CO2함량유소변화,염도범위위17～24 wt%적NaCl(혹자34～36 wt%적MgCl2),균일온도위152～195℃.포과체적수거결합탄산염지질온도계현시미교대작용적압력범위시180～320MPa(7～12km),철교대작용적압력범위시280～420MPa(10～16km),설명지열제도약위25～35℃/km.포과체침출액적분석표명Cl/Br화Na/Br적비치존재변화,단잉구설명부미적서수래원시상이첩기화하삼첩기적분류증발암래원.철질탄산염류체적고추화고전함량,설명재철교대과정중주위흑색편암적명현영향.릉미광화철교대작용,표명교대류체중적탄화이양화탄,주요시해양침적적래원.릉철광적"Sr/86Sr비치((0.71124～0.71140),설명송적다래원,최초응시석탄기화이첩기적해수,단타피당지기타륙각중적송혼염.
Kosice deposit is the second biggest magnesite deposit in Slovakia (150 Mt), located in the eastern part of the Gemeric unit. The main Mg-carbonate body is hosted by Carboniferous limestone and dolomitic limestone, while footwall black schists contain thin carbonate lenses replaced by Fe-carbonates. Paleozoic rocks were affected by low-grade metamorphism (chlorite zone) during Variscan orogeny (M1). Mg-replacement started with the crystallization of dolomite 1, followed by magnesite and terminating by formation of Fe-magnesite along cracks. Fe-carbonates include early ankerite-dolomite, ankerite and later siderite with calcite and quartz. Based on carbonate geothermometry dolomite 1 crystallization occurred at 300 ～ 340℃, which is supported by the M1 metamorphic mineral assemblage (chlorite, muscovite-illite). Ankerite crystallization occurred at 320 ～370℃. Minor veinlets with dolomite 2, chlorite and illite-phengite represent younger mineral assemblage of the M2 metamorphism, attributed to Alpine orogeny.Fluid inclusion (FI) study in magnesite showed the presence of brines of variable composition (mostly 21 to 42 wt% NaCl eq.)with high concentration of salts other than NaCl, and variable amount of dissolved CO2. Homogenization temperatures (Th) ranged from 164 to 217℃ in two-phase aqueous FIs and 217 to 344℃ in halite(?)-bearing FIs. CO2-rich FIs (1 ～22 wt% NaCl eq. , CO2 where they co-exist with halite-bearing inclusions. CO2 shows increased participation in fluids in later stages of Mg-replacement. Quartz associated with Fe-carbonates contained only two-phase aqueous brine FIs (17 to 24 wt% NaCl eq. or 34 to 36 wt% MgCl2 eq. , Th 152 to 195℃) with variable amount of dissolved CO2. Combined with carbonate geothermometry, FI data imply pressure ranges for Mgreplacement ～ 180 to 320 MPa (7 ～ 12 kn) and for Fe-replacement ～280 to 420 MPa (10 ～ 16 kn), suggesting a thermal gradient of about 25 to 35℃/kn.Leachate analyses of fluid inclusions showed variable Cl/Br and Na/Br ratios, but the fractionated evaporitic origin of Mg-rich brines (Upper Permian and Lower Triassic) is still suggested. High Br and I content in Fe-carbonate fluids indicates appreciable influence of surrounding black schists on the Fe-replacement process.Carbon (δ13CPDB= - 1 to + 3.7‰) and oxygen (δ18OSMOW = 12.5 to 17.5 ‰) isotopes from magnesite and from carbonates in Fe-replacement suggest predominantly marine sedimentary origin of carbon and CO2 in the replacement fluids. 87 Sr/86 Sr ratio of magnesites (0.71124 to 0.71140) indicates variable sources of Sr, where the original Carboniferous and Permian seawater Sr ratio was modified by other local crustal sources of Sr.
