关于密西西比河谷型(MVT)铅锌矿床的一些探讨

密西西比河谷型(MVT)铅锌矿床是全球最重要的铅锌矿床类型之一,由于其储量大、开发早,在成矿规律研究等方面均取得了重要进展,如成矿物质来源、成矿流体的驱动机制、成矿金属的迁移机制和沉淀富集机制、成矿时代、成矿模式等。文章在总结前人研究成果的基础上,主要从含矿建造和区域盆地卤水活动两个方面对MVT矿床的成矿规律进行了系统的总结和综合研究,厘定了MVT矿床的含矿建造,主要包括特定的含矿岩性组合、盆地中的红层、生烃层等,分析了区域盆地卤水活动对MVT矿床的制约,主要包括区域白云石化与MVT铅锌矿床的空间分布关系、与MVT铅锌矿床常伴生的其他类型矿床,并对MVT铅锌矿床的成因进行了初步的探讨。最后,认为特定的岩性组合(特别是砂岩、碳酸盐岩、泥页岩组合)、含矿岩系下部碎屑岩的褪色蚀变、区域红层盆地的广泛发育、生烃盆地的边缘、区域白云石化的前锋地带等,是MVT矿床及其伴生矿床找矿勘探的重要参考依据。     

密西西比河谷型(MVT)铅锌矿床:认识与进展

MVT铅锌矿床作为一种重要的沉积型铅锌矿床类型一直受到人们的重视,近年来取得了许多重要进展,主要体现在6个方面:①MVT铅锌矿床研究范围逐渐扩大,在全世界发现了诸多相关矿床,多归为其亚类;②提出该类矿床主要分布在造山带的前陆盆地、逆冲推覆带等构造挤压环境,少数产于陆内伸展环境,改变了MVT矿床与板块构造无关的观点;③放射性同位素测年和古地磁测年技术广泛应用,获得了大量成矿年龄数据,表明MVT矿床主要形成在显生宙石炭纪—早三叠纪和白垩纪—第三纪两个时期,与地球演化史上全球尺度的板块会聚时间密切相关;④流体包裹体研究揭示了成矿流体温度主要为90~150℃,盐度w(NaCleq)为10%~30%,成矿流体具有盆地卤水特征,卤水源自近地表蒸发海水或围岩蒸发盐,同位素资料反映Pb来自地壳岩石,S来自地壳岩石或沉积物中残留的硫酸盐。成矿流体驱动机制包括构造挤压和重力驱动两种;⑤古地磁和生物化学标志物判定,单期热液活动可能持续几千到几万年,而整个矿床形成可能持续几个到十几个百万年;⑥矿质沉淀机制主要有3种:流体混合、硫酸盐还原和还原硫机制,不同成矿环境可能受不同机制控制。     

甘肃代家庄铅锌矿床地质特征

代家庄铅锌矿床位于下拉地—西成铅锌成矿带上,赋存于中泥盆统碎屑岩夹碳酸盐建造中。矿床受地层、岩性、岩相、构造等因素的控制,属沉积改造型矿床。本文通过对代家庄铅锌矿床地质特征及成矿规律的综合研究,总结了控矿因素和找矿标志,以期为矿床评价和外围找矿提供依据。     

水城青山铅锌矿床地质特征及控矿因素初探

通过对青山铅锌矿矿床的地质特征分析,对比水城中部地区威水背斜南西翼各段的地质特征,论述了背斜倒转翼的层间小褶曲,多组断裂共同控制了青山铅锌矿床产出的规律,并以此为指导指出了寻找“青山式”矿床一些找矿标志。     

青山-横塘矿区铅锌矿床控矿断裂特征及找矿评价

黔西北铅锌成矿区海西期经历了北西向水城断陷的发育演化,沉积了巨厚的泥盆系、古炭系地层,形成区域内主要的矿化层位。青山－横塘矿区位于威水铅锌成矿带之水城中部矿田,区内构造发育,成矿条件有利,产出了青山、横塘等中小型矿床,从矿区内控矿断裂的同生活动特征分析,断陷盆地内ＮＷ 断裂的同生活动控制了矿带,活动较强烈地段控制了矿区,ＮＥ向断裂的同生活动控制了矿床。     

特提斯域的密西西比河谷型(MVT)铅锌矿床

特提斯域是全球最重要的密西西比河谷型(MVT)铅锌矿床富集区,矿床广泛地分布在陆-陆碰撞造山带两侧的陆块上,就位于碰撞形成的褶皱-逆冲带和前陆带内,成矿通常发生在碰撞挤压作用晚期或之后、区域处于走滑或伸展的阶段。矿床、矿体的就位与张性断裂密切相关,主要控矿因素有蒸发盐底辟构造、碳酸盐岩溶蚀垮塌构造、蒸发盐溶蚀垮塌构造、高孔隙度白云岩、含重晶石地层等。油气流体在许多矿床和矿集区出现,其主要通过与硫酸盐发生反应为铅锌成矿提供还原硫。陆-陆碰撞的大地构造环境、大量的蒸发盐、丰富的油气流体是特提斯域富集MVT矿床的重要原因,域内寻找MVT矿床的潜力巨大。     

河北蔡家营铅锌（金银）矿床地质特征

该矿区位于华北地台北缘,是一个产于变质岩中的火山热液型多金属矿床。锌和伴生金、银、砷、镉均达大型规模,铅、硫等矿也达中型规模以上。矿体呈不规则的脉状产出,多成群出现,彼此平行,矿体较为集中。矿石主要有绿泥石一闪锌矿型及绢云母-多金属型两类。前者富锌,易选,局部含金较高;后者富铅和银,较难选,含砷较高。矿床的主要控矿条件是:①矿体产于多次活动的断裂构造带之中;②矿化作用主要与燕山期中酸性次火山岩(石英斑岩)有关,次火山岩密集分布区矿化甚佳;③太古界红旗营子群的角闪斜长变粒岩中锌、铅、金、银的丰度很高,为潜在矿源层;④以黄铁绢英岩为主的围岩蚀变甚为发育。     

湘东南炎陵横岗铅锌矿床地质特征及其找矿标志

横岗铅锌矿位于南岭东西向构造-岩浆成矿带东北缘.通过物化探剖面测量、地质填图、槽探、老隆调查等地质勘查工作,基本查清了炎陵横岗铅锌矿成矿地质特征,总结了矿床成因,认为其应属典型的中温热液裂隙充填型脉状铅锌矿床.在此基础上,预测该矿床具有中型规模找矿远景,并提出了下一步工作的重点区.     

长槽铅锌矿床理想成矿模式

对矿区的导矿、容矿、控矿构造及成矿物质元素的活化、富集、迁移进行系统分析研究，提出矿区的理想成矿模式，用于指导目前的矿山生产、开发及下一步的外围找矿。     

玻利维亚圣克里斯托巴尔银铅锌矿床地质特征

圣克里斯托巴尔矿床位于玻利维亚西南阿尔迪普拉诺高原省乌尤尼（Uyuni）镇西南90 km,矿区海拔约4000 m,是一处与中性至酸性火山岩、次火山岩有关的银-锌-铅矿床。圣克里斯托巴尔地区矿产资源开采历史悠久,西班牙殖民者大约在350年前就开始在该地区开采银矿,近代采矿开始于2001年,该矿床目前由日本住友商事株式会社的全资子公司Monera San Cristobal有限公司运营。矿床探明银、锌和铅的金属储量分别为13.800kt、4.02Mt和1.37Mt,平均品位分别为53×10-6、1.41%和0.48%,是世界上最大露采银矿床之一,2014年共生产312吨银、19万吨锌和6万吨铅。     

Fluorite deposits at Encantada–Buenavista, Mexico: products of Mississippi Valley type processes

Petroleum and aqueous fluid inclusions from the Encantada–Buenavista fluorite mineralized zone in northern Mexico were analyzed by microthermometry, UV fluorescence, Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and Confocal Scanning Laser Microscopy (CSLM) to evaluate the geochemical evolution of the mineralizing fluids. Two-phase (petroleum or brine+vapor) and three-phase (petroleum+brine+vapor) inclusions are described. Aqueous and petroleum-rich inclusions commonly occur in the same plane. Vapor-decrepitated and stretched fluid inclusions are present. A low-salinity methane-saturated fluid and a high salinity-fluid with highly variable methane contents are recognized. H₂S is not quantified but is always detected in close association with methane. Petroleum inclusions are of two types: a low methane petroleum fluid (20 mol%) with low T_h (60 °C) and a petroleum fluid with a methane of content near 30 mol% and a T_h of 90 °C.Pressure and temperature diagrams for the aqueous and petroleum inclusions show three main intersects that allow P–T–X reconstruction of fluid evolution at La Encantada–Buenavista. A CH₄- and H₂S-rich low-salinity brine was mixed with oil that migrated under hydrostatic conditions with a thermal gradient of 70 °C/km. The arrival and mixing of a high-salinity aqueous fluid produced overpressure to 300 bars. A return to hydrostatic conditions was accompanied by an increase in the thermal gradient.The brine related to the fluorite orebodies appears to have a genetic relationship with the brines reported from the Jurassic petroleum basins located west of the fluorite bodies and similarities with reported fluids from Mississippi Valley type deposits. It is interpreted that the fluorine-rich fluids migrated toward the platform margins during the mid-Tertiary (30 to 32 Ma) using extension zones related to Basin and Range tectonism. Mixing of two different brines was responsible for precipitation and mineralization. Heat from magmas, related to tectonic extension, caused decrepitation and changes in the shape of fluid inclusions near the contact zones.     

苏鲁榴辉岩型金红石矿床研究进展

文章对苏鲁榴辉岩型金红石矿床的研究进展进行了简单综述。苏鲁超高压变质带金红石矿床的勘探可追溯到20世纪50年代末，近年来找矿工作取得重要进展，已查明金红石矿床总储量达数千万吨。矿床属典型的榴辉岩型金红石矿床，与超高压变质作用关系密切。金红石在榴辉岩中最主要也最具工业价值的赋存方式是呈粒间颗粒充填于主矿物绿辉石和石榴石之间，金红石中的微量元素与其寄主榴辉岩的类型和产状有明显的相关性，并且可反映其形成温度，因此在苏鲁超高压变质榴辉岩和金红石矿床的研究中具有重要价值。富钛基性原岩是榴辉岩型金红石矿床形成的物质基础，高压区域变质作用是这类矿床形成的必要条件。     

斑岩型钨矿床研究进展

斑岩型钨矿床是全球第三重要的钨矿类型,但对其研究较为薄弱、零散.文章基于团队近年来对斑岩钨矿床的研究并系统搜集了全球的相关资料,然后对其进行梳理与总结.研究表明,斑岩型钨矿主要分布于环太平洋成矿带与阿尔卑斯—喜马拉雅成矿带,岩浆弧、板内及陆-陆碰撞等多种环境均有矿床产出.矿床绝大多数形成于中生代、少量形成于古生代.斑岩...     

Loess stratigraphy of the Lower Mississippi Valley

Loesses of the Lower Mississippi Valley (LMV) are world-famous. Sir Charles Lyell (1847), Hilgard (1860), Stafford (1869), Call (1891) and Mabry (1898), thought the LMV loess was a single water deposit although “double submergence” was noted by Call (1891) and Salisbury (1891). Shimek (1902) and Emerson (1918) recognized LMV loess as a wind deposit which came from the valley. Although wind-deposited loess gained wide acceptance, Russell (1944a) published his controversial theory of “loessification” which entailed weathering of backswamp deposits, downslope movement and recharge by carbonates to form loess. Wascher et al. (1947) identified three LMV loesses, mapped distributions and strongly supported eolian deposition. Leighton and Willman (1950), identified four loesses and supported eolian deposition as did Krinitzsky and Turnbull (1967) and Snowden and Priddy (1968), but Krinitzky and Turnbull questioned the deepest loess. Daniels and Young (1968) and Touchet and Daniels (1970) studied the distribution of loesses in south-central Louisiana. West et al. (1980) and Rutledge et al. (1985) studied the source areas and wind directions which deposited the loesses on and adjoining Crowley's Ridge. B.J. Miller and co-workers (Miller et al., 1985, 1986, Miller and Alford, 1985) proposed that the Loveland Silt was Early Wisconsin rather than Illinoian age and advanced the name Sicily Island loess. They proposed the underlying loess was Illinoian and advanced the name Crowley's Ridge. We termed the loesses, from the surface downward, Peoria Loess, Roxana Silt, Loveland/Sicily Island loess, Crowley's Ridge Loess and Marianna loess. Researchers agree that the surfical Peoria Loess is Late Wisconsin and the Roxana Silt is Late to Middle Wisconsin, but little agreement exists on the age of the older loesses. Pye and Johnson (1988) proposed Early Wisconsin for the Loveland/Sicily Island. McKay and Follmer (1985) suggested this loess correlated with a loess under Illinoian till. Clark et al. (1989) agreed on Crowley's Ridge, but suggested the Loveland/Sicily Island loess on Sicily Island was older. Mirecki and Miller (1994) and Millard and Maat (1994) suggested an Illinoian age for the Loveland/Sicily Island loess. Miller and co-workers suggested, as did Pye and Johnson (1988), an Illinoian age for the Crowley's Ridge loess. McKay and Follmer (1985) suggested it correlated with a loess under “Kansan” till. Stratigraphy indicates the Marianna is the older of the five loesses.

Researchers identified loess on both the east and west side of the LMV as well as on higher terraces within the valley. Many researchers assumed unaltered loesses were commonly yellowish brown, and silts or silt loams (West et al., 1980; Miller et al., 1986). The nonclay fraction of unweathered LMV loesses was dominated by quartz followed * Corresponding author. by carbonates, mainly dolomites, followed by feldspars, and micas. Clays were dominated by montmorillonite followed by micaceous minerals, kaolinite and vermiculite (Miller et al., 1986). Soils in the Crowley's Ridge loess are most developed, followed by the soils in the Loveland/Sicily Island which are more developed than the modern soils in the Peoria Loess. Soils in the Roxana and Marianna loesses are least developed and the Farmdale Soil of the Roxana is the weaker of the two (Miller et al., 1986). There is certainly overlapping range in the degree of soil development in the various loesses.     

Quaternary paleoecology of the Lower Mississippi Valley

In 1938, Clair A. Brown published his classic paleobotanical discoveries from the Tunica Hills of southeastern Louisiana, indicating ice-age plant migrations of more than 1100 km. Brown collected fossils of both boreal trees such as white spruce (Picea glauca) and southern coastal plain plants from deposits mapped as the Port Hickey (Prairie) river terrace by Harold N. Fisk. Subsequent revisions of terrace mapping, radiocarbon dating, and paleoecological analysis reconciled Brown's conceptual and stratigraphic “mixing” of these two ecologically incompatible fossil plant groups. An older Terrace 2 (of Sangamonian to Altonian age) contains the warm-temperate assemblage. A younger Terrace 1 (of Farmdalian, Woodfordian, and Holocene age) includes full-glacial and late-glacial remains of both boreal and cool-temperate plants; and a warm-temperate suite of plants dates from the Holocene interglacial. New plant fossil localities with radiocarbon chronologies are now available from within the Lower Mississippi Valley of Missouri and Arkansas as well as from the adjacent Ozark Plateaus, the Interior Low Plateaus of Kentucky and Tennessee, and the bordering Blufflands of Tennessee, Mississippi, and Louisiana. These studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by regional changes in climate, glacial runoff, and regime of the Mississippi River.     

Pleistocene stratigraphy in the southern Lower Mississippi Valley

Scientific inquiry into Pleistocene stratigraphy of the Lower Mississippi Valley (LMV) dates to early writings of European naturalists in the late 19th century. By the early 20th century, landscape evolution concepts, stratigraphic models, and regional syntheses had developed for most areas. The 1944 monograph of H.N. Fisk marks the advent of a predictive stratigraphic and landscape evolution model that links form and process to a predominantly glacioeustatic mechanism. The Fiskian model gained widespread acceptance, and decades passed before significant alternate models began to emerge. Revised stratigraphic and geomorphic concepts are presently developing from newly acquired environmental and engineering data. Present scenarios classify Pleistocene outcrop areas into erosional and constructional landscapes, and veneers of eolian, colluvial, fluvial, coastal, and marine origin can drape both types of surfaces.

The southern LMV and adjacent Gulf Coastal Plain (GCP) experienced significant landscape change during the Pleistocene. Late Tertiary (Pliocene?) to Early Pleistocene deposition of the Upland Complex was by streams with a high sand and gravel load relative to its mud load. The regional drainage network and fluvial system behavior was probably significantly different from the modern. Braided stream alluvial fan complexes received sediment from highland source areas adjacent to the LMV and the glaciated mid-continent. It is plausible that part of Upland Complex deposition predates initial glacial advances.

From Early to Middle Pleistocene, an erosional landscape formed during a dissection period that chiefly postdates soil formation on stable landscape positions of the Upland Complex. Slope evolution truncated a regionally extensive geosol in multiple phases, and parts of the erosion surface complex are graded to the oldest preserved constructional alluvial plains in present valleys. Toe and foot slope positions of the erosion surface complex and its correlative alluvial plains are presently delineated as the Intermediate Complex. Constructional landscapes formed at this time are sparsely preserved; Fisk's Montgomery Terrace in the Lower Red River Valley (LRRV) is the best preserved example. Influences on the development of erosion surfaces in the LMV are not well understood; however interactions of relative sea level fall, climate change, and epirogenic crustal movement are plausible factors.

From the latter part of Middle Pleistocene to the Holocene, there was widespread evolution of modern constructional landscapes. Constructional alluviation preserved lithofacies of mixed load, laterally accreting, meandering streams that developed over large areas of the southern LMV to form parts of the Prairie Complex. Lateral planation in valleys and stable rates of upland sediment generation were dominant processes during Prairie Complex deposition.

Pleistocene stratigraphic examples considered important by Fisk are still considered relevant to modern stratigraphic investigators. Presently, Pleistocene units of the southern LMV, the adjacent LRRV, and central GCP can be correlated only by relative stratigraphic relationships. Refined chronostratigraphic and paleoenvironmental models for these areas would help improve the understanding of the geomorphic influences on Quaternary landscape evolution in the region.     

斑岩型钼矿床研究进展

文章总结了北美西部及中国斑岩型钼矿床的研究成果,介绍了斑岩型钼矿床的分类、共生岩浆岩、矿化方式及蚀变特点,重点探讨了斑岩型钼矿床的成矿流体特点,钼在岩浆-热液系统中的富集沉淀机制以及斑岩型钼矿床的成矿物质来源。     

Mechanism of sulfide mineralization through successive metasomatic replacement stages of zoned host dolomite in Cracow-Silesian Zn-Pb deposits (Mississippi Valley type), Pomorzany Mine,Poland

Replacement of dolomite rhombs is zone selective in Cracow-Silesian Zn-Pb deposits. The discussed replacement of dolomite by sphalerite occurs as spotted sphalerite ore constituting about one-fourth of the economic sulfide mineralization of the Pomorzany Mine. Replacement is controlled by two factors, i.e., microporosity and chemical composition. The epigenetic host dolomite rhombs are zoned into three main zones, i.e., the outer rhombohedral rim which is hard and Fe rich with remarkable Zn content, the inner zone which is porous and Zn rich but usually low in Fe content, and the core of the dolomite rhombs which is Fe free but may contain some Zn. Zones rich in Zn were the first to be replaced by sphalerite; the same holds true for zones with higher microporosity showing a high degree of crystallographic disorder of cations. The other zones seem to be intact. There are four successive replacement stages, i.e., partial, moderate, intense, and advanced. During replacement the intact parts become more Zn-rich, consequently being replaced completely in the later stages, the greater the zinc content in the host dolomite is, the more reactive it is to replacement by sphalerite. The liberated iron from replaced Fe-rich zones is fixed as finely crystalline pyrite.