Stratabound Ore Deposits Research Articles

STUDY ON THE DUCTILE DEFORMATION DOMAIN OF THE SIMPLE SHEAR IN ROCKS——TAKING BRITTLE FAULTS OF THE COVERING STRATA IN THE SOUTHERN JIANGSU AREA AS AN EXAMPLE

A study on the ductile deformation domain of the brittle fault in the shallow level ofthe crust is a new probe field for the modern structural geology. Taking the southern Jiang-su Province area as an example the orientation measurement of quartz crystals, the com-positional texture observation of three pressure sensitive minerals and the rheological param-eter determination of dislocation densities, etc. have been demonstrated and analysed basedon typical samples in the present paper. In addition, their generation mechanisms arealso discussed from the cataclastic rheology, the dynamic differentiation and the simpleshearing, specially, from the Ode strength theory. Finally, a generative relationship betweenthe ductile deformation domain of the brittle fault system, in the regional layer--slip andthe formation of the stratabound ore deposit is shown as well.

Palaeogeographic reconstruction of sandstones using weighted mean grain-size maps, with examples from the Karoo Basin (South Africa) and the Sydney Basin (Australia)

Although sandstone grain-size maps can be a powerful means of reconstructing ancient depositional environments, they have rarely been used in the past. In this paper, two case studies are presented to illustrate the potential of this technique where other, more conventional methods may not be applicable. In the first case, a braided to anastomosing river system in the Triassic Molteno Formation of the South African Karoo Basin is examined. The weighted mean grain-size map clearly portrays the distribution of channels and islands and compares very well with other methods of reconstruction. The second case study examines an offshore shoal in the Permian Nowra Sandstone of the Sydney Basin in Australia. Here the grain-size map shows a north-northeasterly trend parallel to the orientation of the shoal, with a zone of coarsest grains displaced to the east of the shoal crest. This probably reflects the location of the breaker zone. As grain size is an important factor controlling the porosity and permeability of sediments, these maps can provide very useful information when exploring for epigenetic, stratabound ore deposits such as uranium, or planning production wells for oil and gas.

Lower carboniferous paleokarst in the Carnic Alps (Austria, Italy)

In the Carnic Alps of Austria and Italy a broad spectrum of distinct paleokarst features of Lower Carboniferous age has been recognized, including an extensive paleorelief at the surface dated mainly by conodonts, collapse breccias, silcrete horizons, fissures and strata-bound ore deposits; in the subsurface are caves with cave sediments and paleo-karst-related cements. The paleokarst is associated with the unconformity that separates the Devonian to Lower Carboniferous limestone sequences from the overlying flysch deposits of the Hochwipfel Formation. In terms of the currently used conodont zonation, this event occurred during theScaliognathus anchoralis-Doliognathus latus zone, which corresponds to the latest Tournaisian or the Tournaisian/Visean boundary in Belgium. Field observations as well as biostratigraphic, microscopic and isotopic data establish a sequence of events which explain the karst features observed within a spatial and temporal framework. A drop in sea-level during the Late Tournaisian resulted in extensive limestone dissolution and karstification at surface and subsurface levels, and in local formation of fissures, caves and breccias. Almost simultaneously, a high-porosity silcrete regolith developed at the surface, exhibiting characteristic microporous and alveolar textures and composite void fillings of a euhedral quartz, chalcedony and mosaic quartz. Spar calcite coating on the cave walls may represent original speleothems, which predate the densely laminated and predominantly fine grained cave sediments. These and radial fibrous calcite in the fissures were generated in a phreatic environment. Finally, a slow rise in sea-level promoted the formation of crystal silt and clastic internal sediment in fissures, leading to the formation of rubble pack breccias and the transgression of the Hochwipfel Formation. Their high content of radiogenic strontium (plus other indications) rather suggest a crystalline rock source than a sea-water or host rock origin.

Formation of strata-bound ore deposits in China: studies on fluid inclusions

Fluid inclusion studies were made on the basis of the geological data on the strata-bound ore deposits of China including those of Pb, Zn, Au, Ag, Sb, U, Hg, W, quartz-crystal and sparry calcite. An attempt was made to approach the model of formation for each type of ore deposits by considering the material sources, the migration of fluids and the conditions of mineralization. It is found that ore-forming fluids (especially H2O) originate as heated underground water reacts with the wallrocks and dissolves Na+, Ca2+, K+, Cl+, HCl− and Mg2+. The ore-forming elements and other components including sulfur are derived mainly from the wallrocks. The ore fluids are mainly of NaCl−Ca−HCO3−H2O system with salinities ranging from 4 to 14 wt.% NaCl equivalent and densities ranging from 0.9 to 1.0 g/cm3. It may be concluded that the deposits were formed at temperatures ranging from 150 to 250°C under pressures from 300 to 1000 bars. Ore deposition may have been controlled by temperature and pressure or by the mixing among different fluids.

Stratabound ore deposits related to synsedimentary tectonics: South-West Sardinia (Italy) and Sierra de Aracena (Spain); a comparison

Deposition of stratabound Zn-Pb-Ba ores in the Lower Cambrian carbonates in South-west Sardinia show a distinct relation with the prominent tensional tectonics in the area. A part of the mineral deposits are syngenetic (sedimentary-exhalative), other massive sulfides and/or barite are early diagenetic. Other occurrences (MVT) are from early to late-diagenetic. They are mostly confined to matrix- and cementbreccias which might be dependent on the Cambrian tectonics.

Boron isotope evidence for the involvement of non-marine evaporites in the origin of the Broken Hill ore deposits

IDENTIFYING the palaeogeographic setting and mode of origin of stratabound ore deposits can be difficult in high-grade metamorphic terranes, where the effects of metamorphism may obscure the nature of the protoliths. Here we report boron isotope data for tourmalines from the early Proterozoic Broken Hill block, in Australia, which hosts giant lead-zinc-silver sulphide deposits. With one exception the 11B/10B ratios are lower than those for all other tourmalines from massive sulphide deposits and tour-malinites elsewhere in the world. We propose that these low ratios reflect leaching of boron from non-marine evaporitic borates by convecting hydrothermal fluids associated with early Proterozoic continental rifting. A possible modern analogue is the Salton Sea geothermal field in California.

Finite‐Element Simulation of Long‐Term Transient Regional Ground‐Water Flow

ABSTRACTA finite‐element model is developed to solve the two‐dimensional, transient, ground‐water flow equation on a regional scale over geologic time for the purpose of assessing the rate of hydraulic head decay at depth in response to erosional modifications of the land surface. The model includes a time‐stepping procedure that allows consideration of sedimentary basins with large hydraulic conductivity contrasts. Results confirm that hydraulic head patterns that are not in equilibrium with existing topography can persist at depth over geologically significant periods of time. A sensitivity analysis on a hypothetical layered system shows that the rate of hydraulic head adjustment, due to erosional modifications of the topography, is particularly sensitive to the thickness, continuity, and vertical hydraulic conductivity of the low‐permeability layers. Application of the two‐dimensional model to the Red earth region of northern Alberta, Canada predicts response times that are reduced by two‐thirds over those predicted with one‐dimensional models. The concept of delayed hydraulic response over geologic time has important implications in the siting and design of nuclear waste repositories, the analysis of contaminant plume migration, and the use of the hydrodynamic approach to the exploration for petroleum resources and stratabound ore deposits.

Facies control of strata-bound ore deposits in carbonate rocks: The F-(Pb-Zn) deposits in the Alpine Triassic of the Alpuj�rrides, southern Spain

The strata-bound fluorite-(barite-)Pb-Zn ore deposits occurring within the more than 3,000 m thick Alpujarride Carbonate Formation of the Betic Cordillera, southern Spain, are linked to two defined stratigraphic positions (within the Anisian and at the Ladinian-Carnian transition) and to definite sedimentary contexts. These are highly restricted lagoons isolated from the open sea by calcarenitic barriers with noticeable development of algal mats in their inner margins. Preevaporitic deposition conditions are usually recognized. The ore-bearing horizons are located either at the transition from evaporitic to normal marine deposition (as in the case of the Anisian ore-bearing horizon) or at the transition from normal marine to evaporite deposition (as in the case of the uppermost Ladinian to lowermost Carnian ore-bearing horizon). These vertical facies changes correspond also to the transitions from predominantly terrigenous (continental and/or coastal) sedimentation to marine carbonate sedimentation (Anisian ore deposits) and vice versa (upper Ladinian-lower Carnian). It is proposed that the ore deposits in the Triassic Alpujarride Formation are controlled by certain facies associations in the lagoonal environment. The depositional environment determines the hydrologic regimes responsible for early diagenetic formation of fluorite and of the related ore minerals in a way similar to that of early-diagenetic dolomite. This hypothesis is consistent with field and petrographic observations and with available geochemical and itotopic data reported in other works. The present investigation intends to underline the role played by surface-linked ore formation processes, i.e., by ore-forming processes essentially linked to the environments in which sedimentation and early diagenesis takes place, in the genesis of numerous strata-bound Zn-Pb-(F-Ba) ore deposits in carbonate rocks.

A contribution to the ore genesis of the magnesite deposit of Eugui, Navarra (Spain)

In the area of the magnesite deposits of Eugui (Navarra, Spain) studies on illite crystallinity, the degree of graphitization of carbonaceous material, measurements of vitrinite reflectivity, and fluid inclusions have been carried out on dolomites, magnesites, schists, and carbonaceous matter. These rocks have suffered metamorphism of very low to low grade. The magnesite appears generally concordant with the Namurian dolomitic rocks showing a typically banded structure. The genetic model proposed involves an early Mg concentration during sedimentation (syndiagenetic dolomitization), lateral circulation of saline solutions, and formation of diagenetically crystallized rhythmites (DCR), and final compaction. The formation of magnesite took place under the conditions of low pressure and temperatures close to 150°C, very similar to all strata-bound ore deposits. Deformation and regional metamorphism only caused minor removal, recrystallization, and transformation of the clay minerals and carbonaceous matter.

A study on the behavior of mercury in weathering environment in Wanshan district

Studies on the mechanism of supergenic dispersion, migration and enrichment of mercury and other elements in strata-bound ore deposits are of great importance both in theory and in practice. In special reference to the Wanshan mercury ore deposits, this paper discusses the mechanism of supergenic migration of mercury and the associated elements lead, zinc, antimony, etc. In this paper the focus of the discussion is placed on the existing forms of mercury, the rules governing the migration and enrichment of mercury and associated elements in the process of weathering and some aspects of the simulating experiments on weathering of carbonate rocks. Three existing forms of mercury are recognized in carbonate rocks. The migration of mercury together with the associated elements in the process of weathering follows the sequence: SiO2→Pb→Hg→Sb→Zn. The results of simulating experiments on weathering of carbonate rocks show that weathered materials contain more mercury and associated elements than the original rocks.

Potential Exploration Targets for Roxby Downs-Olympic Dam Type Mineral Deposits: ABSTRACT

The Olympic Dam deposit near Roxby Downs, central South Australia, appears to be another type of sediment-hosted stratabound ore deposit. It contains copper, gold, silver, uranium, and rare earths, and in terms of present market prices, is valued at over $100 billion, making it one of the world's most valuable deposits. When brought on line in 1988, the projected production of 4,000 tons/year of U3O8 as a by-product will have a significant impact on the world uranium market. The deposit is hosted in middle Proterozoic rocks in a deep, small basin within the Gawler craton, and is overlain by 350 m (1,148 ft) of unmineralized late Proterozoic miogeoclinical Adelaidean sediments on the Stuart shelf. The nearest host rocks are no closer than 150 km (93 mi). According to Western Mining Corporation, the discovery resulted from regional considerations, with target selection being decided by nearly superimposed gravity and magnetic highs identified from detailed geophysical studies. The present study is a synthesis and integration of large amounts of geological, geophysical, and geochemical data available from the South Australian Department of Mines and Energy, mining companies, and universities. The presence of a probable analog deposit at Mt. Painter, approximately 270 km (168 mi) east-northeast of Olympic Dam, available for field study and sampling, makes possible the testing of ideas and hypotheses. The exposed Gawler craton and surface and drill core samples from Mt. Painter have supplied materials for further study. Plate tectonic reconstructions of the Gawler craton make it possible to apply Olympic Dam genetic models to other continents. The present study undertakes this application to the United States resulting in several areas being interesting targets. End_of_Article - Last_Page 853------------

Theoretical analysis of the role of groundwater flow in the genesis of stratabound ore deposits; 1, Mathematical and numerical model

Carbonate-hosted lead-zinc deposits of the mississippi valley type are thought to have formed through the migration of warm (50 degrees -150 degrees C) subsurface fluids in sedimentary basins. The fundamental role of fluid flow is poorly understood; depending on the stage of evolution of a basin, either a compaction-drive or gravity-drive fluid-flow system may be developed. Quantitative examination of the role of one flow mechanism in ore genesis; gravity-driven groundwater flow. Equations governing fluid flow, heat transport, mass transport, and geochemical mass transfer. Numerical modeling techniques are used to develop a computer code for simulation of regional transport processes along cross sections. The finite-element method is applied to solve the steady-state, fluid-flow, and heat-transport equations, and a moving-particle random-walk algorithm is developed to predict the advection and dispersion of aqueous species.--Modified journal abstract.

Theoretical analysis of the role of groundwater flow in the genesis of stratabound ore deposits; 2, Quantitative results

Sensitivity analysis indicate that gravity-driven groundwater flow systems are capable of sustaining favorable fluid-flow rates, temperatures, and metal concentrations for ore formation at groundwater-discharge areas near the edge of a basin. Under a gravity-drive mechanism, groundwater flows from recharge areas in the elevated regions of a foreland basin to discharge areas in lower-elevation regions. Flow patterns and rates are largely dependent on the basin geometry, the water-table configuration, and the subsurface variation in permeability.--Modified journal abstract.

Lithofacies features and mechanism of formation of “Zihe-type” time- and strata-bound iron ore deposits in central Shandong province

The Lower Palaeozoic system is a series of iron-bearing rocks consisting mainly of shallow sea-fades carbonates. On the basis of microfacies analysis of the carbonate rocks, the Lower Palaeozoic sedimentary sea basin is divided into two broad sedimentary-tectonic regions of four sedimentary facies and eight subfacies. The original iron-rich carbonates were deposited in saltlakes, lagoons, etc. of the restricted basins. Over the long geological history, the original iron formations were reconstructed to various extents by late tectonic processes. Geological observations and studies on the equilibrium mechanism of oxygen/sulfur isotopic fractionation and the composition and temperature of fluid inclusions in the minerals indicate that thermal brines played an important role in reworking of the original iron-rich carbonate rocks, which led to the formation of sedimentary-reworked strata-bound ore deposit.

Elements and element association in sedimentary-reformed ore deposits

The sedimentary-reformed ore deposit is one of the main types of strata-bound ore de-posits. The elements for the formation of sedimentary-reformed ore deposits in Chinamainly include Pb, Zn, Hg, Sb, As, U, Cu, Fe as well as S(pyrite), F(fluorite), Ba(barite)and Si(crystal). In this paper, the background content values of ore-forming elements inthese deposits are summarized, the association types of ore-forming elements in these depositsdivided and the geochemical characteristics and formation mechanism of these associationtypes discussed.

Cobalt as an exploration tool in the Outokumpu zone, Finland

Cobalt as an exploration tool in the Outokumpu zone, Finland

Stratabound lead-zinc pyrite ore deposits in upper precambrian carbonate rocks, Rodna Mountains, Romania

The Blazna-Guset mining area is located in the Rodna Mountains, Eastern Carpathians, North Romania. It is mostly covered by the metamorphic rocks of the Rebra Series (Upper Precambrian; K/Ar dating gave 800 m.y.). The middle part of this series — called the Carbonate Formation — contains lead-zinc pyrite ores hosted by prevailingly carbonate rocks. The ores form flat and thin lenses occurring together with fine intercalations of silicate-, graphite- and quartz-bearing rocks within the calcite-dominated limestones. Pyrite, ironpoor sphalerite and galena are the main ore minerals. Chalcopyrite, pyrrhotite and magnetite also occur in small amounts. Within the highly deformed and partly recrystallized parts of the ore bodies bournonite, arsenopyrite and pearceitepolybasite were locally encountered. Ba, Ti and Mn are the most significant ore-accompanying elements.

Preliminary study of REE iron formations in China

Geological and geochemical characteristics of REE iron formation (REEIF), a term proposed by Prof. Tu Kuang-chih to specify a special type of Precambrian iron formations rich in REE, are discussed in this paper with special reference to its REE contents, REE distribution patterns, the formation mechanism, the relationship between its development and the multi-stage evolution of the continental crust in China, and the implications of REE as an indicator of oxidation state for ancient atmosphere. Major conclusions are outlined as follows: (1) REEIFs are characterized by high REE concentrations against the very low REE levels in normal Precambrian iron formations. (2) REEIFs are formed by marine sedimentary-diagenetic processes in miogeosynclines or transition zones during Proterozoic times To some extent, volcanic activity may play an important role in the deposition of ore-forming materials. In a broader sense, REEIFs belong to Fe-bearing dolomite formations. Most REEIFs in China may be superimposed by late geological processes such as hydrothermal-metasomatism, migmatization and metamorphism. Generally, REEIFs have much in common with stratabound ore deposits in respect to their characteristic features. (3) Similar to Precambrian iron formations, REE are enriched in LREE. But, the degree of LREE enrichment is noticed to increase of total REE content. Most REEIFs are characterized by high ratios of σ Ce/σY, (Mg+Fe)/Ca, Na/K, Nb/Ta, Zr/Hf, Th/U, Ba/Sr, etc. (4) The extensive occurrence of REEIFs indicates higher REE abundance in the continental crust of China, thus lending further support to the multi-stage theory regarding the evolution of chemical elements and the differentiation in the continental crust of China. (5) Preliminary data seem to support the time-dependence of REE distribution patterns and relative Eu contents of REEIFs in China.

A preliminary study on the mechanism and physico-chemical conditions of formation of Gongchangling rich iron deposit

Field observations and results of experimental studies show that the Gongchangling rich iron deposit is characterized by multigenesis as a result of repeatition of different geological processes. It probably resulted from the infiltration of silica under the influence of aqueous solutions derived from migmatite-granite. Because the formation of rich iron deposit was accompanied by the formation of skarn minerals and the transformation of sedimentary-metamorphic poor iron deposits, characteristics of both skarn deposits and stratabound ore deposits can therefore be recognized. Experimental data indicate that physico-chemical parameters of formation of the rich iron deposit areP=2kbar,T=500–600°C, pH=8–10, and\(f_{O_2 } = 10^{ - 25} \) bar.

In situ metal-staining of biological membranes in sediments

Decomposition of organic matter in sediments is principally mediated by bacteria and burrowing organisms. During this process, organic matter undergoes a series of structural chances in which heavy metals and minerals actively participate1–4. Metal–organic complexes arise which are instrumental in crystal seed formation and growth of authigenic minerals such as sulphides, phosphates, oxides and carbonates. By means of transmission electron microscopy, modern organic-rich sediments from the Black Sea and Lake Tanganyka and samples from Eocene Messel oil shale in Germany were studied for the presence of heavy metal stained biological membranes. We report here that during early diagenesis heavy metals seem to supplant hydrogen, alkali and alkaline-earth ions placed at the surfaces of membranes in living organisms. The resulting patterns are the same as those found in organic tissues which before electron microscopy were stained with lead, uranium and osmium salts. In sediments, naturally stained membranes can further act as templates for mineral deposition and may—in certain environmental conditions—lead to strata-bound ore deposits.