Mississippi Valley-type Lead-zinc Deposits Research Articles

Distribution and Formation of Mississippi Valley–Type Lead–Zinc Deposits on the Eastern Margin of the Siberian Platform (Results of GIS Analysis of the Global Crust Model)

Recent studies of the lithosphere based on the gravity data from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) were used for the first time to analyze the distribution patterns and formation of the Mississippi Valley–Type (MVT) lead–zinc deposits on the eastern margin of the Siberian Platform. MVT deposits occur on the flanks of the large Lena–Vilyui oil and gas province. A GIS analysis of the model of the structure of the Earth’s crust showed that the spatial distribution of MVT deposits coincides with the areas where the Moho surface (asthenosphere) rises. These deposits are attributed to the medium temperature area of the upper mantle and controlled by abnormally deep troughs (about 2 km) of the upper horizon of the lithospheric sedimentary layer indicated by seismic speeds. The hybrid geothermal-hydrocarbon mineral-forming system could play an essential role in forming MVT lead–zinc deposits.

A review of the types and ore mechanism of the cobalt deposits

<p indent=0mm>Cobalt is an important strategic metal of major industrial countries. In order to invoke the importance of the cobalt deposits to the strategic industries in China, this paper aims to introduce the different types of the cobalt deposits in the worldwide, to review the ore mechanism of the cobalt deposits and to propose the research directions of the future studies for the cobalt deposits. Global cobalt resources can be grouped into two deposit types: terrestrial and seafloor deposits. The major terrestrial cobalt deposits include sediment-hosted stratiform copper-cobalt, nickel-cobalt laterite, and magmatic sulfide copper-nickel deposits. Other sources include black shales hosted, skarn and replacement, metasedimentary rocks hosted, iron oxide copper-gold deposits, volcanic massive sulfides, polymetallic veins (five-element veins and other vein types), and Mississippi Valley-Type lead-zinc deposits. Seafloor cobalt-related deposits are mainly iron-manganese-cobalt nodules and crusts, which are hardly explored and productive. The detailed information of the major cobalt deposits is also listed, presenting the tonnage and grade of various types of the cobalt deposits in China. The polymetallic veins and black shales hosted types have the highest grade, and both types should be paid more attentions during the mineral exploration. For the geochemical behavior of the cobalt during the magmatic and hydrothermal environment, the partition coefficient of cobalt in the process of mantle melting under different tectonic background and water contents are relatively stable. Also, during the fractional crystallization of ultramafic-mafic magmas in the magmatic sulfide deposits, cobalt has a slight preference for olivine relative to basalt. In hydrothermal ore system, aqueous Cobalt(II) chloride complexes play a crucial role in cobalt transport and deposition, and their solubility has a close relationship with the temperature and salinity of the fluids. The debate on the genesis of various cobalt-rich deposits can be considered as the debate on the evaluation between diagenetic and superimposed processes in the ore formation. Besides some polymetallic veins, black-shale hosted, Mississippi Valley-Type lead-zinc, and iron oxide copper-gold deposits, the process of cobalt enrichment has close relationships with the ultramafic-mafic intrusions or volcanic during the magmatic processes, hydrothermal processes, or weathering. Moreover, the multiple-stage hydrothermal processes are also critical to cobalt enrichment. We suggest that the spatial-temporal distribution of different cobalt deposits in China and how their formations are related to the tectonic evolution of the craton and orogenic belt should be investigated immediately to determine the controlling geological factors in different cobalt deposits. Also, the thermodynamic properties of different cobalt-bearing speciation under different physico-chemical environments should be identified. The relationship between geodynamic processes and formation of cobalt-rich deposits needs to be considered. Finally, great attention should be paid to the study of marine iron-manganese-cobalt nodules and crusts and their proper mining technology.

Trace elements in sphalerites from the Mississippi Valley-type lead-zinc deposits around the margins of Yangtze Block and its geological implications: A LA-ICPMS study

扬子板块周缘铅锌多金属成矿带内分布着数以百计的沉积岩容矿型铅锌矿床，它们不仅是我国主要的铅锌矿产地，同时也是重要的稀散元素（Ge、Ga等）生产基地。本次研究采用LA-ICPMS技术分别测定了扬子板块西南缘的会泽铅锌矿床、金沙厂铅锌矿床、大梁子铅锌矿床，扬子板块北缘的马元铅锌矿床以及扬子板块东南缘的凤凰茶田锌（铅）汞矿床中闪锌矿的微量元素组成，以揭示闪锌矿中微量元素（稀散元素）的富集规律和赋存状态，并为矿床成因类型的厘定及稀散元素矿产资源综合利用提供更多依据。LA-ICPMS微量元素测定结果显示闪锌矿中不同微量元素（稀散元素）分布不均匀，但这些矿床中闪锌矿总体以富集稀散元素Ge、Ga、Cd，贫In、Se、Tl、Te为特征，其Fe、Mn含量要明显低于与岩浆热液有关的高温闪锌矿，指示了扬子板块周缘铅锌矿床可能形成于中-低温成矿流体，而与岩浆热液无直接的成因联系，此外这些矿床中闪锌矿富Ge贫In的特征与其他的密西西比河谷型铅锌矿床（MVT）一致。同时，本次研究综合分析了闪锌矿中不同微量元素（稀散元素）之间的相关关系，并与闪锌矿微量元素LA-ICPMS时间分辨率特征相结合，研究表明：这些铅锌矿床中稀散元素Ge可能主要通过3Zn2+↔Ge4++2（Cu+，Ag+）和2Zn2+↔Ge4++□（晶体空位）的替代方式进入闪锌矿，Ga在闪锌矿中富集机理主要为2Zn2+↔（Cu，Ag）++（Ga，As，Sb）3+。此外，为进一步揭示不同成因类型铅锌矿床中稀散元素的富集规律，本文还系统对比了全球范围内不同类型铅锌矿床闪锌矿的稀散元素（均为LA-ICPMS数据）组成特征，并初步探讨了造成不同成因闪锌矿中稀散元素（Ge、Ga和In）差异性富集的主要控制因素，研究表明：（1）Ge在中低温盆地卤水成矿系统（MVT和SEDEX矿床）和岩浆-火山热液成矿系统（浅成脉状铅锌矿床和VMS矿床）形成的闪锌矿中均可能富集成矿，但中低温浅成脉状矿床中Ge的富集程度要明显高于高温脉状矿床，指示了成矿温度是控制闪锌矿中Ge富集的一个重要因素。（2）铅锌矿床闪锌矿中In主要为岩浆来源，In倾向于在成矿温度较高的岩浆及火山热液成因铅锌矿床中富集成矿，而壳源的MVT和SEDEX型铅锌矿床中闪锌矿均贫In。可见除形成温度外，成矿物质来源是决定闪锌矿是否富In的关键因素。（3）除矽卡岩型铅锌矿床外，其他不同成因类型、不同形成温度的铅锌矿床中闪锌矿均可能富Ga。矽卡岩型铅锌矿床闪锌矿具有明显的贫Ga、Ge的特征，这可能是由于矽卡岩化过程中稀散元素Ga、Ge大量进入早期矽卡岩矿物，进而导致了成矿流体以及随后形成的闪锌矿中Ga、Ge的贫化。综上所述，闪锌矿中稀散元素富集与否和富集程度受成矿物质来源、成矿流体性质以及流体演化过程等多因素的综合控制。（4）扬子板块周缘铅锌矿床闪锌矿的微量元素（稀散元素）组成特征指示了它们形成于中低温成矿环境，稀散元素的富集规律与其它MVT型铅锌矿床类似。

Distribution of trace elements and Pb isotopes in stream sediments of the Tri-State mining district (Oklahoma, Kansas, and Missouri), USA

Mississippi Valley-Type (MVT) lead-zinc deposits, which account for 24% of the global resources of Pb and Zn, are found throughout the world with the largest deposits occurring in North America. The Tri-State Mining district, located at the intersection of Oklahoma, Kansas, and Missouri, was one of the most productive Pb and Zn districts during the turn of the 20th century.The current geochemical study of ore samples from the Tri-State district and of stream-sediment samples collected from selected sites from the lower Arkansas River drainage basin (the Neosho River, Tar Creek, and Spring River) show that the effect of past mining activity and leaded gasoline on Pb concentrations in the river sediment can be readily documented. Lead isotopic ratios of leachates of stream sediments from the Tar Creek area collected downstream from Picher, OK, correlate well with those of ore samples from the Tri-State Mining District, suggesting that most of the Pb adsorbed onto the stream sediments was sourced by the ores. Lead isotope measurements of leachates delimit the extent of high Pb concentrations in the Tar Creek region caused by mineralization and mining at Picher, OK. The effects of mining are noticed to a lesser extent in the Spring and Neosho rivers, with increasing distance from Picher. The influence of the leaded gasoline is more pronounced with increasing distance from the superfund site, contributing between around 52% and 68% extractable Pb to the stream sediments 14 km from the Picher mining area. This discovery can have major implications in how to evaluate the risk to human and animal health, as well as guide remediation efforts in this region.Leachates from stream-sediment samples collected from the Spring and Neosho rivers show lower Pb isotopic ratios than the Tar Creek leachates and plot outside the field defined by ore samples from the Tri-State Mining District. They fall along an array defined by a binary mixture of Pb from the leaded gasoline and the Pb sourced from the Tri-State mining district, indicative of two distinct Pb sources.There is a gradual decrease in the Zn, Pb, As, and other heavy-metal concentrations in the stream sediment leachates with distance from the mines. The Zn concentration reaches a maximum of 1592 ppm in the Picher area, more than 29 times the average natural background levels in the Tri-State region (41 ppm). About 24 km downstream from Picher, the Zn concentrations decrease substantially to values lower than both, normal crustal abundance and background levels. Similarly, the Pb concentration is highest in the Picher area (326 ppm), about 14 times the natural background levels in the Tri-State region (16 ppm), and it drops to much lower values downstream. Even though the highest Cu and As concentrations are seen in the Picher area (10 ppm and 1.44 ppm, respectively), they are lower compared to the natural background levels for the region (11 ppm and 6 ppm, respectively).

Age and Origin of the Well-Preserved Organic Matter in Internal Sediments from the Silesian-Cracow Lead-Zinc Deposits, Southern Poland

The molecular and petrographic characteristics of organic matter in internal sediments from the Mississippi Valley-type lead-zinc deposits in southern Poland reveal immature and well-preserved organic matter. Huminite reflectance values of organic matter in all internal sediments are low, with a mean value of 0.29%, corresponding to a lignite range of coalification. Most organic compounds in the organic matter (e.g., cadalene, retene, simonellite, perylene, and β -sitosterol and its transformation products stigmastanol and stigmasta-3,5-dien-one), as well as lignin degradation compound products (e.g., benzoic acid, vanillin, 4-benzaldehyde, benzenedicarboxilic acids, and hydroxybenzoic acids), are of terrestrial origin. Monosaccharides with dominant α - and β -glucose were identified as possible remnants of cellulose degradation products, suggesting an excellent state of organic matter preservation, given that monosaccharides are preserved only under conditions of limited oxygen after sedimentation, resulting from the rapid accumulation of internal sediments in meteoric paleokarst cavities followed by insignificant diagenesis. Petrologic and palynological data on internal sediments clearly indicate a Middle Triassic age for organic matter and for the development of a Triassic meteoric karst system immediately after Anisian carbonate sedimentation.

Volcanogenic Massive Sulfide Occurrence Model

W.C. Pat Shanks III and Roland Thurston, Editors. PP. 363. U.S. Geological Survey Scientific Investigations Report 2010–5070–C. 2012. Downloadable from . This is one of a series of ore deposit models, written by scientists of the U.S. Geological Survey, which at present include contributions on Mississippi Valley-type lead-zinc deposits (Leach et al., 2010) and porphyry copper deposits (John et al., 2010). The stated purposes of this VMS model are as follows: (1) for national assessment of the mineral potential for these deposits in the United States, and (2) to assist exploration geologists, students, and teachers of economic geology, and researchers interested in understanding the origin of this important deposit type in the context of earth history and plate tectonics. Among the latter group is a large international group of scientists studying the distribution, characteristics, and origin of VMS deposits on the modern seafloor. Most of the stages of VMS exploration, mining, and remediation are covered well in this volume. Exploration begins with …

Changes in sub‐water table fluid flow at the end of the Proterozoic and its implications for gas pulsars and MVT lead–zinc deposits

AbstractA fundamental change in the nature of sub‐water table fluid flow occurred at roughly the Proterozoic–Phanerozoic boundary when organic matter began to be buried in sufficient quantities that nonaqueous fluids could occupy a significant fraction of the pore space. This allowed the formation of remarkably durable capillary seals that could trap gas in large portions (hundreds of kilometers) of a basin for hundreds of millions of years. Gas loss from these gas zones can be highly dynamic, especially during gas generation. Under the right circumstances, hundreds of cubic kilometers of gas can be rapidly discharged into adjacent permeable aquifers. In Pennsylvanian/Permian time, the Arkoma Basin may have repeatedly discharged such volumes of gas into the very permeable Cambrian sandstone and karstic carbonate aquifers of the mid‐continent of the United States. This could have displaced brines rapidly enough to form the Mississippi Valley‐type (MVT) lead–zinc deposits of this age that are associated with the Arkoma Basin, heating them only briefly as required by maturity indicators. Sea level rise accompanying the melting of Permian continental glaciers may have triggered the gas expulsion events. This radically new mechanism for the formation of MVT deposits is just one example of the nonlinear dynamics of gas accumulations that are possible since Late Proterozoic time.

Base- and precious-metal deposits in the Basin and Range of Southern California and Southern Nevada—Metallogenic implications of lead isotope studies

Southern California and southern Nevada contain abundant lead–zinc deposits with strikingly different characteristics. On the west, the Darwin Terrane contains abundant Jurassic and Cretaceous intrusions surrounded by lead–zinc skarn and replacement deposits rich in pyrite and manganese minerals. The Tecopa Terrane is east of the Darwin Terrane and contains some lead deposits that are hosted by the Proterozoic Noonday Dolomite. These lead deposits have no consistent relation to igneous rocks; they contain mainly galena, and are devoid of pyrite and manganese minerals. Other skarn and vein deposits in the Ivanpah and Tecopa districts are more closely associated with igneous rocks. Mississippi Valley type lead–zinc deposits are present still farther to the east in the Goodsprings Terrane in Nevada. These deposits are hosted by breccias formed below the Mississippian–Pennsylvanian unconformity and are unrelated to igneous rocks. Deposits in the Darwin Terrane have lead isotopic signatures that lie along a mantle–sediment mixing line indicating that they formed in a continental arc setting analogous to that for the plutons in the Sierra Nevada batholith [Chen, J.H. and Tilton, G.R., 1991. Application of lead and strontium isotopic relationships to the petrogenesis of granitoid rocks, central Sierra Nevada batholith, California. Geological Society of America Bulletin 103, 439–447]. Encroachment of this continental arc on the North American continent in the eastern part of the Darwin Terrane resulted in a lead isotopic signature that is like that of the strongly contaminated plutons [Chen, J.H. and Tilton, G.R., 1991. Application of lead and strontium isotopic relationships to the petrogenesis of granitoid rocks, central Sierra Nevada batholith, California. Geological Society of America Bulletin 103, 439–447]. Many deposits from the Inyo Mountains on east side of the Owens Valley have lead isotopic signatures that reflect this encroachment. To the east in the Tecopa Terrane, encroachment of the continental arc on the Mojave crust resulted in partial melting of 1.7 Ga amphibolite and granulite facies rocks to produce the plutons and mineral deposits associated with plutons in this terrane. Lead from deposits in this terrane hosted in the Proterozoic Noonday Dolomite and associated rocks have a lead isotope signature that reflects hydrothermal circulation of fluids in the Mojave supracrustal rocks. The boundary between the Darwin Terrane and the Tecopa Terrane lies just west of the Ash Valley–Panamint Range Fault and is bounded by the Towne Fault on the north and the Garlock Fault on the south. Lead isotopic data from the Goodsprings district in southwestern Nevada, east of the Tecopa Terrane, form a 1.45 Ga linear array that is indicative of Mississippi Valley type mineralization. Although we have no independent evidence of the timing of the tectonic events that formed these deposits, it is likely that all formed as a result of the Mesozoic collision of the Panthalassen crust with the North American continent.

Reply to Discussion on "Mississippi Valley-type lead–zinc deposits through geological time: implications from recent age-dating research" by S.E. Kesler and C.W. Carrigan (2001) Mineralium Deposita 36:711–740

Reply to Discussion on "Mississippi Valley-type lead–zinc deposits through geological time: implications from recent age-dating research" by S.E. Kesler and C.W. Carrigan (2001) Mineralium Deposita 36:711–740

Discussion on "Mississippi Valley-type lead–zinc deposits through geological time: implications from recent age-dating research" by D.L. Leach, D. Bradley, M.T. Lewchuk, D.T.A. Symons, G. de Marsily, and J. Brannon (2001) Mineralium Deposita 36:711–740

Discussion on "Mississippi Valley-type lead–zinc deposits through geological time: implications from recent age-dating research" by D.L. Leach, D. Bradley, M.T. Lewchuk, D.T.A. Symons, G. de Marsily, and J. Brannon (2001) Mineralium Deposita 36:711–740

Mississippi Valley-type lead–zinc deposits through geological time: implications from recent age-dating research

Remarkable advances in age dating Mississippi Valley-type (MVT) lead–zinc deposits provide a new opportunity to understand how and where these deposits form in the Earth's crust. These dates are summarized and examined in a framework of global tectonics, paleogeography, fluid migration, and paleoclimate. Nineteen districts have been dated by paleomagnetic and/or radiometric methods. Of the districts that have both paleomagnetic and radiometric dates, only the Pine Point and East Tennessee districts have significant disagreements. This broad agreement between paleomagnetic and radiometric dates provides added confidence in the dating techniques used. The new dates confirm the direct connection between the genesis of MVT lead–zinc ores with global-scale tectonic events. The dates show that MVT deposits formed mainly during large contractional tectonic events at restricted times in the history of the Earth. Only the deposits in the Lennard Shelf of Australia and Nanisivik in Canada have dates that correspond to extensional tectonic events. The most important period for MVT genesis was the Devonian to Permian time, which corresponds to a series of intense tectonic events during the assimilation of Pangea. The second most important period for MVT genesis was Cretaceous to Tertiary time when microplate assimilation affected the western margin of North America and Africa–Eurasia. There is a notable paucity of MVT lead–zinc ore formation following the breakup of Rodinia and Pangea. Of the five MVT deposits hosted in Proterozoic rocks, only the Nanisivik deposit has been dated as Proterozoic. The contrast in abundance between SEDEX and MVT lead–zinc deposits in the Proterozoic questions the frequently suggested notion that the two types of ores share similar genetic paths. The ages of MVT deposits, when viewed with respect to the orogenic cycle in the adjacent orogen suggest that no single hydrologic model can be universally applied to the migration of the ore fluids. However, topographically driven models best explain most MVT districts. The migration of MVT ore fluids is not a natural consequence of basin evolution; rather, MVT districts formed mainly where platform carbonates had some hydrological connection to orogenic belts. There may be a connection between paleoclimate and the formation of some MVT deposits. This possible relationship is suggested by the dominance of evaporated seawater in fluid inclusions in MVT ores, by hydrological considerations that include the need for multiple-basin volumes of ore fluid to form most MVT districts, and the need for adequate precipitation to provide sufficient topographic head for topographically-driven fluid migration. Paleoclimatic conditions that lead to formation of evaporite conditions but yet have adequate precipitation to form large hydrological systems are most commonly present in low latitudes. For the MVT deposits and districts that have been dated, more than 75% of the combined metal produced are from deposits that have dates that correspond to assembly of Pangea in Devonian through Permian time. The exceptional endowment of Pangea and especially, North America with MVT lead–zinc deposits may be explained by the following: (1) Laurentia, which formed the core of North America, stayed in low latitudes during the Paleozoic, which allowed the development of vast carbonate platforms; (2) intense orogenic activity during the assembly of Pangea created ground preparation for many MVT districts through far-field deformation of the craton; (3) uplifted orogenic belts along Pangean suture zones established large-scale migration of basin fluids; and (4) the location of Pangea in low latitudes with paleoclimates with high evaporation rates led to the formation of brines by the evaporation of seawater and infiltration of these brines into deep basin aquifers during Pangean orogenic events.

Origin of iron-rich Mississippi Valley–type deposits

Research Article| January 01, 2001 Origin of iron-rich Mississippi Valley–type deposits James St. Marie; James St. Marie 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Stephen E. Kesler; Stephen E. Kesler 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Cameron R. Allen Cameron R. Allen 2Cominco American, Inc., 15918 East Euclid Avenue, Spokane, Washington 99216-1815, USA Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (1): 59–62. https://doi.org/10.1130/0091-7613(2001)029<0059:OOIRMV>2.0.CO;2 Article history received: 22 Feb 2000 rev-recd: 04 Oct 2000 accepted: 04 Oct 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation James St. Marie, Stephen E. Kesler, Cameron R. Allen; Origin of iron-rich Mississippi Valley–type deposits. Geology 2001;; 29 (1): 59–62. doi: https://doi.org/10.1130/0091-7613(2001)029<0059:OOIRMV>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The abundance of iron in Mississippi Valley–type lead-zinc deposits and districts varies greatly; some deposits contain large amounts and others are almost free of iron. Iron in Mississippi Valley–type deposits is largely paragenetically early pyrite or marcasite that was replaced by sphalerite and galena, often in the central part of the deposit or district. Sedimentary exhalative and Irish-type base metal deposits, which also form from basinal brines, have similar variations in iron content. Calculated metal contents of brines in equilibrium with galena, sphalerite, and pyrite show that iron is significantly more abundant than lead and zinc in high-temperature (>200 °C), relatively acid brines with low sulfur contents, whereas zinc dominates under most other conditions, including brines with high temperatures and high sulfur contents. These results suggest that iron-rich Mississippi Valley–type deposits form from brines expelled from the deepest, hottest parts of sedimentary basins. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Abstract: Regional Association of Petroleum Productive Breccias, Mississippi Valley Type Lead-Zinc Deposits and Sedex Deposits; Strategy for Exploration of Albion-Scipio (150 + Mmbbls) Type Deposits

Abstract: Regional Association of Petroleum Productive Breccias, Mississippi Valley Type Lead-Zinc Deposits and Sedex Deposits; Strategy for Exploration of Albion-Scipio (150 + Mmbbls) Type Deposits

A Critical Review of Theories on the Origin of Mississippi Valley-Type Lead-Zinc Deposits in the North American Midcontinent: ABSTRACT

A Critical Review of Theories on the Origin of Mississippi Valley-Type Lead-Zinc Deposits in the North American Midcontinent: ABSTRACT

COPPER-LEAD-ZINC: Role of geophysics in exploration for MVT lead-zinc deposits on the Lennard Shelf, Western Australia

The exploration strategy in the search for Mississippi Valley-type (MVT) mineralisation on the Lennard Shelf has been modelled on the approach commonly used in exploration for similar mineralisation in North America. Regional areas of interest are defined using a combination of geology, geochemistry and geophysics, then systematically grid-drilled. Several MVT lead-zinc deposits have been discovered on the Lennard Shelf through the application of this strategy. Mississippi Valley-type lead-zinc deposits are difficult geophysical targets. Their geophysical characteristics have been studied on the Lennard Shelf to provide a guide for more cost-effective exploration both on the Lennard Shelf and elsewhere. On a regional scale, gravity and aeromagnetic surveys, used in conjunction with geochemistry, effectively focus exploration into favourable structural and lithological settings. Detailed gravity and seismic surveys delineate areas of the host carbonates in regions of shallow cover. Several known Mississippi Valley-type deposits and prospects on the Lennard Shelf are associated with extensive marcasite haloes and associated induced polarisation anomalies. In areas of shallow cover, the induced polarisation method can be used to cost effectively define prospective areas by mapping mineralised systems on a semi-regional scale. These areas can then be tested using grid drilling.

Role of Geophysics in Exploration for MVT Lead-Zinc Deposits on the Lennard Shelf, Western Australia

The exploration strategy in the search for Mississippi Valley-type (MVT) mineralisation on the Lennard Shelf has been modelled on the approach commonly used in exploration for similar mineralisation in North America. Regional areas of interest are defined using a combination of geology, geochemistry and geophysics, then systematically grid-drilled. Several MVT lead-zinc deposits have been discovered on the Lennard Shelf through the application of this strategy. Mississippi Valley-type lead-zinc deposits are difficult geophysical targets. Their geophysical characteristics have been studied on the Lennard Shelf to provide a guide for more cost-effective exploration both on the Lennard Shelf and elsewhere. On a regional scale, gravity and aeromagnetic surveys, used in conjunction with geochemistry, effectively focus exploration into favourable structural and lithological settings. Detailed gravity and seismic surveys delineate areas of the host carbonates in regions of shallow cover. Several known Mississippi Valley-type deposits and prospects on the Lennard Shelf are associated with extensive marcasite haloes and associated induced polarisation anomalies. In areas of shallow cover, the induced polarisation method can be used to cost effectively define prospective areas by mapping mineralised systems on a semi-regional scale. These areas can then be tested using grid drilling.

Fluid flow and heat transport in the upper continental crust

Abstract The upper 10–15km of the continental crust is saturated with aqueous brines and is sufficiently permeable to allow the circulation of these fluids. The most important driving forces for fluid flow in the continental crust are topography gradients, sediment compaction and diagenesis, and buoyancy forces. Topographically-driven flow is generally the most efficient mechanism for mass and heat transport, and therefore has recently been favoured in theories of the origin of Mississippi Valley-type lead-zinc deposits. The magnitude of heat transport by fluid movement in the crust has an exponential dependence upon the depth of circulation. In areas of the continental crust with appreciable topography gradients ( c. 0.01) and permeabilities greater than c. 10 −17 m 2 , the background thermal state will likely be appreciably perturbed by groundwater movement. Fluid circulation in the upper crust is both continuous and pervasive due to topography and fluid-density gradients. The old conception of the continental crust as an unchanging body of solid rock should be replaced by a paradigm that recognizes the continental crust as a two-component system; a solid framework which continuously evolves through thermal, chemical, and mechanical interaction with crustal fluids.

Catastrophic release of heat and fluid flow in the continental crust

Research Article| January 01, 1992 Catastrophic release of heat and fluid flow in the continental crust David Deming David Deming 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Geology (1992) 20 (1): 83–86. https://doi.org/10.1130/0091-7613(1992)020<0083:CROHAF>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation David Deming; Catastrophic release of heat and fluid flow in the continental crust. Geology 1992;; 20 (1): 83–86. doi: https://doi.org/10.1130/0091-7613(1992)020<0083:CROHAF>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Heat may be released catastrophically from the continental crust by the onset of free convection in orogenic zones. Orogeny itself could create the conditions necessary for free convection by increasing the permeability of the crust. In the specific case of a continental collision zone, the conditions favoring free convection may move progressively into continental interiors, perhaps to repeated episodes of convection and related thermal events. Simple models and assumptions suggest that individual episodes of convection circulation and heat release persist for periods of time of the order of 106 yr or less. The rate and magnitude of energy release depend upon the initial thermal state and permeability of the crust and the depth of fluid circulation. Estimates made from typical parameters indicate that the total thermal energy released from the crust is approximately equivalent to an increase of background heat flow from about 60 to 200 mW/m2 for a period of 106 yr. A significant amount of this heat can be transported into the interior of a continent by a gravity-driven flow system if a continuous aquifer of sufficient permeability is present. The hypothesis could explain several phenomena attributed to tectonically driven fluids associated with the Alleghenian-Ouachita orogeny. These include the formation of Mississippi Valley-type lead-zinc deposits, widespread potassic alteration, and remagnetizations. Although speculative, the hypothesis is consistent with our current state of knowledge concerning the extent of fluid circulation in the continental crust. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Thermal constraints on basin‐scale flow systems

An important constraint on basin‐wide flow systems is the thermal regime. Studies of high temperatures above fault zones which penetrate geopressured sediments and heat flow in orogenic zones have been used to document both pathways and velocities of pore fluid movement. Similarly, the high temperature (100–150°C) at shallow depths (&lt;1.5km) inferred from studies of fluid inclusions associated with Late Paleozoic Mississippi Valley‐type (MVT) lead‐zinc deposits places a very restrictive constraint on their formation by regional fluid migration. We have used numerical models of fluid and heat transport to evaluate the viability of sediment compaction by overthrusting and topographically driven recharge as driving mechanisms for regional fluid migration. Sediment compaction by overthrusting leads to Darcy velocities on the order of cm/yr, too low to have significant effects on the temperature field unless flow is channelized. Topographically driven recharge can lead to fluid velocities on the order of m/yr. However, it is difficult to achieve the extremely high temperatures (100–150 °C) at shallow depths (&lt;1.5km) associated with MVT deposits unless heat flow values greater than 100 mW/m2 are used. Thus, there are fundamental limitations on the ability of either mechanism to continuously transport large amounts of heat for millions of years on a basin‐wide scale. Temporal or spatial focusing of flow is likely to have played a critical role in the genesis of phenomena such as MVT deposits.

The organic geochemistry of two mississippi valley-type lead-zinc deposits

The organic matter associated with two Mississippi Valley-type deposits (Gays River, Nova Scotia, and Shullsburg, southwestern Wisconsin) has been characterized by petrographic, isotopic, spectrophotometric, gas chromatographic, and mass spectral methods. Comparisons were made of distributions of organic species identified from unmineralized and mineralized samples. The primary variations in the distributions of organic species isolated from the two deposits reflect variations in host-rock paleoecology, facies, and geologic age. Secondary effects were microbial degradation, thermal maturation, and mineralization. Mineralization in both deposits caused an increase in the concentrations of low molecular weight hydrocarbons.The genetic model tested in this study presumed that mineralizing brines evolved from sedimentary basins and migrated to the ore host rocks. This model implies that an epigenetic generation of organic matter should occur in the deposits. In the Gays River deposit, the probable aquifer for the mineralizing solutions contained an organic distribution markedly different from the indigenous organic matter in the host reef and can be interpreted as a second, epigenetic organic fraction added to the deposit. Evidence was not observed for an epigenetic organic generation in the Shullsburg deposit. The thermal maturity of the organic matter in the Wisconsin district supports a previous estimate of 0.25 m.y. to form a major orebody in the district.