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1.
云南文山官房钨矿床团山矿段围岩蚀变与矿化规律研究   总被引：1，自引：0，他引：1  
云南省文山县官房白钨矿床属于中—大型矽卡岩型白钨矿床。矿区内围岩蚀变强烈,蚀变分带明显,依据蚀变岩岩相学及岩石化学测试结果,并结合钻孔编录资料,将团山矿段围岩蚀变划分为3个蚀变带,自花岗岩体向外依次为金云母-绿帘石化带→透辉石-透闪石化带→镁橄榄石化带。通过对各蚀变带中岩石组分迁移量分析认为:在团山矿段热液蚀变及白钨矿化过程中,来自花岗质岩浆热液的A l2O3、S iO2、TFe、K2O、Na2O迁入,灰岩(白云质灰岩)中MgO、CaO迁出,团山矿段白钨矿化主要发生在透辉石-透闪石化带中,矿体产状与透辉石-透闪石带产状基本一致,橄榄石化带中钨矿化相对较弱,金云母-绿帘石化带中仅可见零星钨矿化。这一研究成果将对文山官房钨矿床成矿规律研究以及矿区进一步找矿提供重要的理论依据。  相似文献   

2.
云南省巧家县东坪铅锌矿床大地构造位置处于扬子地台西南缘,是滇东北地区一个典型的铅锌矿床。矿体赋存于震旦系灯影组白云岩中,呈脉状、似层状,并受断裂构造和Si/Ca面控制,矿石矿物以方铅矿、闪锌矿为主,近矿围岩蚀变有硅化、白云石化、黄铁矿化。硫、铅同位素分析显示,成矿流体的硫源主要是赋矿地层中的海水硫酸盐经热化学还原作用而成,铅来自壳源。岩石原生晕特征显示：成矿过程具有多阶段叠加,早期成矿作用以铅为主,并有微弱的锌矿化,而后受铅矿化强烈的叠加改造作用;钻孔S5ZK001→ZK001→S4ZK001近矿晕元素Pb、Zn组分从南西到北东向呈由浅部到深部的分布规律;钻孔ZK001→ZK701-1→ZK1701→ZK3901亦为由浅部到深部的分布规律;以ZK001为中心,向南东、北东矿体埋深加大,在北东部（S4ZK001）及南东部（ZK3901）深部还具有一定的找矿潜力。  相似文献   

3.
Quartz Al–Mg granulites exposed at In Hihaou, In Ouzzal (NW Hoggar), preserve an unusual high-grade mineral association stable at temperatures up to 1050°C, involving the parageneses orthopyroxene–sillimanite–garnet–quartz, sapphirine–quartz and spinel–quartz. The phase relationships within the FMAS system show that a continuum exists between the earlier prograde reaction textures and those of the later decompressive event. The following mineral reactions involving sillimanite are deduced: (1) Grt+Qtz→Opx+Sil, (2) Opx+Sil→Grt+Spr+Qtz, (3) Grt+Sil+Qtz→Crd, (4) Grt+Sil→Crd+Spr, (5) Grt+Sil+Spr→Crd+Spl, (6) Grt+Sil→Crd+Spl, (7) Grt+Crd+Sil→Spl+Qtz and (8) Grt+Sil→Spl+Qtz. Minerals in quartz Al–Mg granulites display compositional variations consistent with the observed reactions. The Mg/(Mg+Fe2+) range of the main minerals is as follows: cordierite (0.81–0.97), sapphirine (0.77–0.88), orthopyroxene (0.65–0.81), garnet (0.33–0.64) and spinel (0.23–0.56). The reaction textures and the evolution of the mineral assemblages in the quartz Al–Mg granulites indicate a clockwise P–T trajectory characterized by peak conditions of at least 10 kbar and 1050°C, followed by decompression from 10 to 6 kbar at a temperature of at least 900°C.  相似文献   

4.
Dalli Cu–Au porphyry deposit was occurred in the igneous diorite, quartz diorite porphyry (QDP), and volcanic rocks such as porphyritic amphibole andesite, andesite (AND), dacite, and pyroclastics during the late Miocene to Pliocene. Regolith investigations and Advanced Spaceborne Thermal Emission and Reflection Radiometer images were used to identify the anomalous areas. According to lithogeochemical survey (from boreholes and trenches) in Northern Dalli Cu–Au porphyry, the potassic, chlorite, sericite, propylitic, and argillic alterations have been found and mineralization was basically associated with potassic and quartz–sericite alterations. The alteration is dominantly moderate quartz chlorite?±?sericite magnetite with 1–10 mm wide quartz?±?magnetite veinlets. The elevated copper–gold values are correlated with density of stockworking and mineralization. The intensity of the mineralization is high in the contact of QDP and AND with increases in pyrite and chalcopyrite values. Malachite, native Cu, and bornite were used to identify supergene, transition, and hypogene zone. In addition, molybdenum increased near to the center of granodiorite intrusion. And besides, from depth to surface in DDH03 and wall rock to mineralization zones, a sequence of Mo→Cu (Au)→Au (Cu) was recorded and the mineralization temperature cooled down (from high to low). The alteration is characterized by specific pattern and structure in Dalli Cu–Au porphyry deposit. The alteration model was followed from the modified Lowell and Gilbert model. The porphyry is stockworked by quartz veins and by quartz magnetite veins. Vein distribution and ore mineralogy vary between the different alteration zones. Due to the formation of an iron cap in the supergene, especially in the southern hills, supergene grade was higher than hypogene zone. Also, hematite, as a dominant Fe oxide in DDH03 borehole with minor limonite, jarosite, and goethite created thickness about 150–270 m in supergene zone; finally, this finding show a possibility of an extensive mineralization.  相似文献   

5.
Amphibole is a rock-forming mineral widely existing on the earth. It is easily dissolved and altered during the later stage of diagenesis and mineralization, and often forms chloritization, which is an important indicator for prospecting. To explore amphibole's dissolution process and alteration mechanism, dissolution experiments were carried out under acidic conditions using pargasite-rich amphibole as raw material, and the effects of temperature, p H, and experiment duration on amphibole alteration were investigated. Experimental samples and products were analyzed using X-ray diffractometer, field emission scanning electron microscope, electron probe micro analyzer, and transmission electron microscopy. It was found that many pores and erosion edges are produced after amphibole dissolution, and there is a clear interface between the dissolved residual portion and the parent. The dissolved residual portion remains in the amphibole phase, but as the temperature and time increase, the intensity of the diffraction peak of the phase in the product decreases, and the peak position shifts to a small angle. Many clay minerals such as chlorite and griffithite formed on the amphibole surface. In an environment with strong acidity(p H=3), the amount of chamosite increases with temperature(180°C→210°C→240°C), whereas clinochlore is only increased in a 150–210°C environment. Griffithite growth was observed in the acidic(p H=6) and low temperature(180°C) environments. Based on this analysis, large radius Cl– enters the amphibole lattice or cracks to promote dissolution. The Al-poor and Ca-and Fe-rich regions between the edge and core of the amphibole are caused by dynamic equilibrium in amphibole dissolution and alteration process, which is an essential indicator for the beginning of amphibole dissolution-alteration. Diffusion and the coupled dissolution-reprecipitation mechanism accomplishes the process of dissolution and alteration to form clay minerals. The energy of the system determined by temperature and p H is the key to controlling the rate of growth and nucleation of clay minerals. High temperature and strong acidity will dissolve more iron from amphibole, which is conducive to chlorite growth. Compared to chlorite, griffithite is more sensitive to temperature. Griffithite attaches on the amphibole surface with a star-like in a weak acid and low-temperature environment. The results of this study can provide a mineralogical basis for the analysis of hydrothermal alteration processes and the division of alteration zones.  相似文献   

6.
The southeastern part of the central Iranian Cenozoic magmatic belt contains many areas with copper mineralization. In an analysis of this region, we used the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Enhanced Thematic Mapper plus (ETM+) images to map the distribution of hydrothermally altered rocks, based on their mineral assemblages. The spectral measurements, based on the field samples and satellite‐image‐derived spectra, show dominantly Al–OH (sericite and clays) and Fe–O absorption features in the visible–near infrared to shortwave infrared regions of the spectrum. Silica–bearing rocks, as well as silicic alteration, show an intense Si–O vibrational feature in the thermal infrared wavelength region. We analyzed ASTER/ETM+ images, performed a directed principal component analysis, and used spectral angle mapper to map areas of hydrothermal alteration and iron oxide/hydroxide minerals. The individual principal component images compiled by directed principal component analysis reveal the distribution of individual alteration minerals such as sericite, kaolinite, chlorite, epidote, and quartz. The best results, in terms of mapping the distribution of alteration, were obtained using the spectral angle mapper method. The altered areas were then sampled and the samples subjected to X–ray diffraction analysis, spectral analysis, and thin sections were observed under a microscope. Field observations reveal that more than 98% of the known copper mineralization occurs within the interpreted alteration areas. The present results indicate the great potential of ASTER and ETM+ data for mapping the distribution of alteration and exploring for copper mineralization in areas with a similar climate and geological setting to those of the present study.  相似文献   

7.
云南哈播斑岩铜(-钼-金)矿床流体包裹体研究   总被引：3，自引：3，他引：0  
哈播斑岩Cu-(Mo-Au)矿床产于哀牢山富碱斑岩带的南段,形成于青藏高原后碰撞阶段构造转换环境,属于陆-陆碰撞型斑岩矿床.根据脉体的交切关系,确定哈播矿床各种脉的演化序列为早期石英脉→石英-黄铜矿脉→石英辉钼矿脉.脉中流体包裹体的岩相学、显微测温和激光拉曼光谱分析等研究结果显示,各期脉中均有富气相包裹体、富液相包裹体和含子矿物多相包裹体,各种包裹体的气相均含有CO2、SO2、H2O等气体.各期脉中多种包裹体并存并具有相似的均一温度范围,富液相包裹体均一温度149～427℃,盐度ω(NaCleq)6.0％～15.0％;富气相包裹体均一温度205～405℃,盐度ω(NaCleq) 3.4％～19.0％;含子矿物多相包裹体均一温度305～516℃,盐度w(NaCleq) 33.5％～61.0％.哈播矿床的初始成矿流体由稳定共存、不混溶的低盐度流体和高盐度流体组成,高盐度流体是哈播矿床成矿元素迁移的主要载体.成矿流体在400℃左右发生“二次沸腾”、分相,温度下降和挥发分持续逃逸可能是Cu-Au成矿的诱因.Mo元素在成矿流体多次沸腾、分相过程中,持续优先分配进入高盐度流体中而逐步富集;温度下降,使含钼硫化物在流体中溶解度降低、沉淀,形成石英-辉钼矿±黄铜矿脉.  相似文献   

8.
马厂箐Cu-Mo-Au多金属矿田位于西南三江复合造山带中段,是带内金多金属矿床的典型代表。矿田内矿化类型复杂,元素组合多样。围绕马厂箐富碱杂岩体矿化类型、元素组合、围岩蚀变呈明显的分带。在岩体中形成斑岩型铜-钼矿床;在岩体与地层内外接触带形成接触交代型(角岩型、夕卡岩型)铜-钼(铁)矿床;在岩体外围地层中形成浅成低温热液金-铅-锌矿床。对应的围岩蚀变表现为自岩体中心向外依次为强硅化带→石英钾长石化带→石英钾长石绢云母化带→夕卡岩化带→中低温热液蚀变。同位素测年结果表明3种类型的矿床成矿均发生于33.7～35.8Ma,金矿床略晚于铜-钼矿床,并与矿田内马厂箐杂岩体侵入时代(33～37Ma)一致。岩矿石的H、O、Pb、S同位素和流体包裹体系统研究表明,从斑岩型铜-钼矿床→接触交代型铜-钼(铁)矿床→浅成低温热液金-铅-锌矿床,矿石中流体包裹体均一温度、盐度和均一压力逐渐降低,成矿物质(矿质和流体)也逐渐从以深部岩浆源为主,演变为以围岩地层和大气降水为主。矿田内不同类型矿床间的时空及成因联系,反映它们是同源岩浆不同演化阶段成矿作用的产物,含矿热液的物化性质及时空迁移决定了它们在不同部位产出不同的矿床类型,构成与富碱斑岩有关的浅成低温热液-斑岩Cu-Mo-Au多金属成矿系统。  相似文献   

9.
The relationship between sporo-pollen color and the degree of maturation of organic matter is discussed with regard to oil generation and evolution, as typified by the Cretaceous system in the Daqing Oil Field, central Songliao Basin, Northeast China. Color variation of spores and pollen is considered as a function of sedimentary environment and thermal alteration. Sporo-pollen color is classified into seven grades, and the degree of thermal alteration is studied in terms of color index. Results show that the sporo-pollen color index for the strata at the depth of 1,000–3,000 m (stratigraphically from the first member of the Liangjiang Formation to the upper Quantou Formation) ranges from 2.5–5.0, corresponding to a palaeotemperature range of 60°–140°C. These are the optimum oil-generating strata. The strata underlying the lower Quantou Formation below 3,000 m with the color index in excess of 5 and the palaeotemperature over 140°C may be favorable for gas accumulation. As for the strata at the depth of less than 1,000 m, i.e., stratigraphically overlying the second member of the Liangjiang Formation, which are characterized by a color index of 1.0–1.5 and a palaeotemperature of less than 60°C, the degree of maturation of organic matter is lower than that in the oil-generating strata.  相似文献   

10.
Hydrothermal ore deposits are typically characterised by footprints of zoned mineral assemblages that extend far beyond the size of the orebody. Understanding the mineral assemblages and spatial extent of these hydrothermal footprints is crucial for successful exploration, but is commonly hindered by the impact of regolith processes on the Earth's surface. Hyperspectral drill core (HyLogger?-3) data were used to characterise alteration mineralogy at the Mt Olympus gold deposit located 35 km southeast of Paraburdoo along the Nanjilgardy Fault within the northern margin of the Ashburton Basin in Western Australia. Mineralogy interpreted from hyperspectral data over the visible to shortwave (400–2500 nm) and thermal (6000–14500 nm) infrared wavelength ranges was validated with X-ray diffraction and geochemical analyses. Spaceborne multispectral (ASTER) and airborne geophysical (airborne electromagnetic, AEM) data were evaluated for mapping mineral footprints at the surface and sub-surface. At the deposit scale, mineral alteration patterns were identified by comparing the most abundant mineral groups detected in the HyLogger data against lithology logging and gold assays. Potential hydrothermal alteration phases included Na/K-alunite, kaolin phases (kaolinite, dickite), pyrophyllite, white mica, chlorite and quartz, representing low-T alteration of earlier greenschist metamorphosed sediments. The respective zoned mineral footprints varied depending on the type of sedimentary host rock. Siltstones were mainly characterised by widespread white-mica alteration with proximal kaolinite alteration or quartz veining. Sandstones showed (1) distal white mica, intermediate dickite, and proximal alunite + kaolinite or (2) widespread white-mica alteration with associated intervals of kaolinite. In both, sandstones and siltstones, chlorite was distal to gold mineralisation. Conglomerates showed distal kaolinite/dickite and proximal white-mica/dickite alteration. Three-dimensional visualisation of the gold distribution and spatially associated alteration patterns around Mt Olympus revealed three distinct categories: (1) several irregular, poddy, SE-plunging zones of >0.5 ppm gold intersected by the Zoe Fault; (2) sulfate alteration proximal to mineralisation, particularly on the northern side of the Mt Olympus open pit; and (3) varying AlIVAlVISiIV–1(Mg,Fe)VI–1 composition of white micas with proximity to gold mineralisation. Chlorite that developed during regional metamorphic or later hydrothermal alteration occurs distal to gold mineralisation. ASTER mineral mapping products, such as the MgOH Group Content used to map chlorite (±white mica) assemblages, showed evidence of correlation to mapped, local structural features and unknown structural or lithological contacts as indicated by inversion modelling of AEM data.  相似文献   

11.
成亚利  周富民  张毅  张三龙 《云南地质》2013,(4):436-438,456
围绕碾沟复式花岗岩和闪长岩,发育一组时间、空间、成因有联系的不同类型矿体——斑岩型、矽卡岩型和沉积改造型.从岩体中心→接触带→围岩,成矿元素显Mo→Cu （Mo） →Pb、En,Ag变化规律.受地层层位及构造控制.  相似文献   

12.
成岩作用及物性演化的研究对致密砂岩储层和致密油开发具有重要意义.综合利用岩石铸体薄片鉴定、扫描电镜、X衍射分析、流体包裹体分析等测试手段,对研究区致密储层进行详细研究.研究表明:深水重力流砂体粒度细,孔喉组合以细孔-微喉型为主,物性差,是一套典型的特低渗透储层;目前正处于中成岩B期,其成岩演化序列为:机械压实作用/方解石胶结→凝灰物质水解蚀变/云母水化/伊利石胶结/绿泥石胶结/石英溶蚀→早期长石溶蚀/石英加大/碳酸盐灰泥重结晶/早期碳酸盐胶结物溶蚀→晚期长石溶蚀→铁方解石胶结,成岩环境主要经历了碱性→酸性→弱碱性的转换过程;距今约99~118 Ma的早白垩世,研究区储层发生了连续的2期油气充注;储层物性演化史表明早成岩期储层的成岩作用对储层物性影响大,使储层已经致密化,研究区具有先致密后成藏的特性.   相似文献   

13.
The Hongtoushan Volcanogenic Massive Sulphide Deposit (VMSD) occurs in the Hunbei granite-greenstone terrane, Liaoning Province, NE China. Rocks in the mining area have been metamorphosed around 3.0–2.8 Ga to upper amphibolite facies at temperatures between 600°C and 650°C. Cordierite-anthophyllite gneiss (CAG) in the Hongtoushan mining area, which occurs hundreds of meters below the ore horizon, corresponds to the metamorphosed semi-conformable alteration zone of the VMSD hydrothermal system, whereas the one immediately below the main ore layer represents the metamorphosed pipe-like alteration zone. Whole-rock oxygen isotope signatures were well preserved in both types of CAGs, although the mineral components have been entirely changed during regional metamorphism. Therefore, whole-rock oxygen isotopes can be used to estimate the formation temperature of both types of alteration zone. Calculations show that the semi-conformable and pipe-like alteration zones for the Hongtoushan submarine hydrothermal system were formed at 290–360°C and 285–320°C, respectively, whereas estimates for the former were slightly higher than that of the latter, indicating that the semi-conformable alteration zone represents the deep part of the Hongtoushan seafloor hydrothermal system, while the pipe-like alteration zone represents the discharge conduits for metal-rich fluids, which is closer to the seafloor.  相似文献   

14.
杨柏林 《地质科学》1988,(2):188-195
本文依据西北某地一次综合性航空遥感试验取得的多光谱图象、热红外扫描图象和微波辐射等遥感资料,结合室内对岩矿测量的反射率、复合介电系数、等效温度等资料,用目视判释法对该区地质问题进行了研究。提出了热红外遥感资料和微波遥感资料对寻找铁和水资源前途,同时对断裂构造的判释也很有意义。  相似文献   

15.
抚顺盆地中-晚始新世古植被与古气候   总被引：1，自引：0，他引：1       下载免费PDF全文
韦一  杨兵  夏浩东  邓会娟 《地球科学》2021,46(5):1848-1861
为重建东北地区中-晚始新世古气候,对抚顺盆地孢粉进行传统鉴定,利用有序聚类分析划分孢粉组合,结合共存分析法对孢粉组合定量化以建立研究区的古气候参数值.鉴定出孢粉67属,划分出（Ⅰ）Quercoidites- Tricolpopollenites- Betulaceoipollenites组合;（Ⅱ）Piceapollis-Tiliaepollenites-Chenopodipollis组合;（Ⅲ）Quercoidites-Betulaceoipollenites-Ulmipollenites组合;（Ⅳ）Pinuspollenites-Abietineaepollenites-Ephedripites组合;（Ⅴ）Betulaceoipollenites-Taxodiaceaepollenites-Quercoidites组合,其中组合Ⅰ、Ⅱ、Ⅲ时代为中始新世;组合Ⅳ、Ⅴ时代为晚始新世.植被类型也经历了:落叶阔叶林-草原型植被→针阔叶混交林-草原型植被→落叶阔叶林-草原型植被→针叶林→针阔叶混交林的转变.气候带经历了由亚热带、亚热带-温带湿润性气候向温带半湿润性气候的转变,年均温和年降雨量均呈降低的趋势,这些变化趋势与全球温度变化趋势相耦合.   相似文献   

16.
Kerogen was isolated from a marine sediment from Tanner Basin, offshore California. Samples of the kerogen were heated under an inert atmosphere at various temperatures and times. The heated and unheated kerogens were subjected to alkaline potassium permanganate oxidation followed by GC/ MS analysis of the products. The kerogens yielded primarily aliphatic C2–C14 α,ω-dicarboxylic acids and benzene mono-to-pentacarboxylic acids. Yields of aliphatic dicarboxylic acids from kerogen decreased with increasing thermal alteration. Yields of benzenecarboxylic acids increased steadily with increasing thermal alteration. The data support the concept that thermal maturation during natural burial of this type of kerogen results in the generation of aliphatic hydrocarbons from an increasingly aromatic residue.  相似文献   

17.
Thermal waters of northern (18°–27°S) and southern (37°–45°S) Chile occur in two very different climatic, geologic and hydrologic environments: arid closed basins with abundant evaporites in the north; humid climate and well drained valleys in the south. The origin and behavior of the main components of the two groups of waters are examined and compared to each other. The modeling of the alteration of volcanic rocks leads to water compositions very different from those observed both in the north and south. In addition to hydrothermal alteration and deep emanations, the Cl/Br ratio reveals a major contribution of saline waters to the two groups: infiltrating brines from salt lakes in the north; seawater in the south.In the north, concentrations of Cl, Br, Na, K, Ca, SO4, Li, B, Si result from the mixing of alteration waters with recycled brines. Hydrothermal alteration is obscured by this massive saline input, except for Mg. δ34S values are consistent with an origin of sulfate from salar brines, which are themselves derived from deep Tertiary gypsum. In the south, two processes account for the composition of thermal waters: mixing of alteration waters with seawater and deep magmatic contribution. The mixing process controls the concentration of Cl, Br, Na, Alk, Si, K, Ca, Mg. Magmatic inputs are detectable for SO4, Li and B. δ34S suggests that sulfate stems from the mixing of alteration waters with either marine SO4 in coastal waters or with deep SO2 in inland waters. In both the north and south, the Mg concentration is drastically lowered (<1 μmol/L) by the probable formation of a chlorite-type mineral. In the south, very small amounts of seawater (<1% in volume) are sufficient to imprint a clear signature on thermal waters. Not only coastal springs are affected by seawater mixing, but also remote inland springs, as far as 150 km from the sea. Subduction of marine sediments in the accretive margin could be the source of the marine imprint in thermal waters of southern Chile. Seawater may be expelled from the subducted lithosphere and incorporated into the mantle source.  相似文献   

18.
Three fractions of organic matter: lipid (benzene:methanol-extractable), humic acid (alkali-extractable) and kerogen (residue) were extracted from a young marine sediment (Tanner Basin, offshore southern California) and heated for different times (5–116 hr) and temperatures (150°–410°C). The volatile (gases) and liquid products, as well as residual material, were then analyzed. On a weight basis, the lipid fraction produced 58% of the total identified n-alkanes, the kerogen fraction 41%, and the humic acid <1%. Whereas n-alkanes produced from lipid show a CPI > 1.0, those produced by thermal alteration of kerogen display a CPI < 1.0. The volatiles produced by heating the lipid and humic acid fractions were largely CO2 and water, whereas those produced from heated kerogen also included methane, hydrogen gas and small amounts of C2–C4 hydrocarbons. A mechanism for hydrocarbon production due to the thermal alteration of organic constituents of marine sediment is discussed.  相似文献   

19.
Gneisses and migmatites of the Gföhl unit (Moldanubian Zone, Bohemian Massif) range from banded mylonitic orthogneiss with recrystallized monomineralic bands, through stromatic (metatexite) and schlieren (inhomogeneous diatexite) migmatite, to isotropic nebulite (homogeneous diatexite). This sequence was classically attributed to increasing degree of anatexis. Under the microscope, the evolution is characterized by progressive destruction of the monomineralic banding that characterizes the original mylonitic orthogneiss. Throughout, the mineral assemblage is biotite–K‐feldspar–plagioclase–quartz ± garnet ± sillimanite, but the mineral compositions exhibit systematic changes with progressive disintegration of the layering. From banded orthogneiss to nebulite, the garnet composition changes systematically, Alm75→94Prp17→0.8Grs2.5→1.2Sps2→11 and XFe = 0.45→0.99 and for biotite, XFe = 0.80→1. This is consistent with a decrease in equilibration temperature and pressure of 790 °C and 8.5–6 kbar, to 690 °C and 5–4 kbar respectively. There is also a systematic change of whole‐rock composition, marked by an increase in SiO2 (71→77 wt%) and XFe (0.62→0.85) and by a decrease in Al2O3 (16→13 wt%) and CaO (1.50→0.43 wt%). Assuming that the rocks started with the same composition, these systematic changes indicate open‐system behaviour. The predicted consequences of various open‐system processes are assessed using thermodynamic modelling. The observed variations are interpreted as being a consequence of melt flow through, and interaction with the rocks, and, to change the rock composition sufficiently, a large volume of melt must have been involved.  相似文献   

20.
《Resource Geology》2018,68(3):209-226
Shin‐Otoyo, Suttsu, Teine, Date, Chitose, and Koryu are sites rich in precious and base metal Miocene–Pleistocene epithermal deposits, and located in southwestern Hokkaido, Japan. The deposits are predominantly hosted by the Green Tuff Formation of Middle Miocene age. Ore petrographic study of these deposits shows the occurrence of variable quantities of Cu–As–Sb–Ag–Bi–Pb–Te sulfosalt minerals. Determination of mineralogical and chemical compositions of the sulfosalt minerals was undertaken to elucidate the time and spatial changes of the sulfide‐sulfosalt minerals. Various types of sulfosalt minerals identified from gold–silver and base metal quartz–sulfide veins represented some sulfosalt mineralization phases, such as the Cu–Fe–Sn–S phase of mawsonite and stannite; Cu–(As,Sb)–S phase of tetrahedrite–tennantite and luzonite–famatinite series minerals; (Cu,Ag)–Bi–Pb–S phase of emplectite, pavonite, friedrichite, aikinite, and lillianite–gustavite series minerals; (Ag,Cu)–(As,Sb)–S phase of proustite–pyrargyrite and pearceite–polybasite series minerals; and Bi–Te–S phase of tetradymite and kawazulite minerals. There are some trends in the paragenetic sequence of sulfosalt mineralization in southwestern Hokkaido (in complete or partial) as follows: sulfide → Cu–Fe–Sn–S → (Cu,Ag)–Bi–Pb–S → (Bi–Te–S) → Cu–(As,Sb)–S → ([Ag,Cu]–[As,Sb]–S). The formation of sulfosalt minerals is characterized by the introduction of some elements such as Sn, Bi, and Te at an earlier stage and an increase or decrease of some elements such as As and Sb, followed by the introduction of Ag at the later stage of ore mineral paragenesis sequence. Mineral composition of the Chitose and Koryu deposits are slightly different from those of Shin‐Otoyo, Suttsu, Teine, and Date due to their lack of Sn (tin) and Bi (bismuth) mineralization. The variable concentrations and relationships are not simply with redistributed trace elements from the original sulfide minerals of chalcopyrite, pyrite, galena, and sphalerite. Some heavier elements were also introduced during the replacement reaction, which is consistent with the occurrence of their associated minerals.  相似文献   

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