Metal Sulfide Ores Research Articles

The role of evaporites in the genesis of base metal sulphide mineralisation in the Northern Platform of the Pan-African Damara Belt, Namibia: geochemical and fluid inclusion evidence from carbonate wall rock alteration

The Otavi Mountain Land is a base metal sulphide ore province in northern Namibia where deposits are hosted by platform carbonates of the Otavi Group in a foreland fold-and-thrust belt on the northern edge of the Pan-African Damara Belt. Deposits have been classified as the Berg Aukas- or Tsumeb-types, based on differences in ore association, stratigraphic position and geochemistry of ores and gangue carbonates. Mineralisation at these deposits is accompanied by carbonate alteration in the form of dolomite and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Based on cathodoluminescence imaging, trace and rare earth element (REE), O and C isotope, and fluid inclusion data, a series of carbonate generations, constituting wall rock alteration around the Tsumeb and Kombat (Tsumeb-type) and Berg Aukas (Berg Aukas-type) deposits, was established. Similar data obtained on the recently discovered Khusib Springs deposit indicate a strong affinity to Tsumeb-type deposits. Tsumeb-type deposits are distinguished from Berg Aukas-type deposits by having trace element and REE concentrations that are significantly higher in the alteration products compared to the carbonate host rocks. Only around Tsumeb-type deposits a relative enrichment in light REE is noted for the hydrothermal carbonate generations that are cogenetic with the main stage of mineralisation. Microthermometric results from fluid inclusions in carbonate alteration phases and associated quartz indicate relatively high salinity (17–23 wt% NaCl equivalent) for the main mineralising and subsequent sulphide remobilisation stages at the deposits investigated. Estimated mineralisation temperatures are significantly higher for Tsumeb-type deposits (370–405 °C) with early sulphide remobilisation in Tsumeb at 275 °C, whereas they are lower at Berg Aukas (up to 255 °C). Fluid inclusion leachate analysis suggests that most of the observed salinity can be ascribed to dissolved, predominantly Ca- and Mg-carbonates and chlorides with subordinate NaCl. Na-Cl-Br leachate systematics indicate a derivation of the fluid salinity from the interaction with evaporitic rocks en route. Tsumeb-type mineralisation is interpreted to be derived from fluids expelled during Pan-African orogeny in the more intensely deformed internal zones of the Damara Belt further south. When the high salinity fluids reached the carbonate platform after having scavenged high concentrations of base metals, base metal sulphide precipitation occurred in zones of high porosity, provided by karst features in the carbonate sequence. Results obtained for the Berg Aukas-type deposits emphasise their derivation from basinal brines, similar to Mississippi Valley-type deposits, and confirm that mineralisation of the Berg Aukas- and Tsumeb-types are both spatially and temporally distinct.

Scale-dependent Electrical Properties of Sulphide Rocks — New Methods and Techniques

A thorough understanding of the the influence of geological factors on electrical petrophysical properties of sulphide orebodies requires careful integration of geophysical and geological measurements at a variety of scales. Two new methods for studying the influence of microscopic and mesoscopic ore textures on electrical properties of sulphide rocks have been developed. Voltage contrast microscopy is a scanning electron microscope technique which enables direct imaging of the effects of an applied potential on a polished rock surface. It has been used to investigate the detailed mechanism of electrical conduction in fine-grained base metal sulphide ores. Initial results suggest that conductive paths may exist along grain boundaries within otherwise resistive minerals, such as sphalerite. Continuity mapping uses a modified flat-bed plotter to directly image the electrical continuity of drill core or hand specimens. A spring-loaded copper electrode traverses the polished sample surface on a grid to produce an image. Electrode movement and potential measurement are fully automated. This technique has been used to study the influence of mesoscopic ore textures on the electrical continuity of massive and disseminated sulphide ore samples. Both new methods are still being developed and refined but initial results suggest that they will usefully complement existing laboratory-based petrophysical techniques.

Physicochemical conditions of deposition and origin of carbonate-hosted base metal sulfide mineralization, Thermes ore-field, Rhodope Massif, northeastern Greece

Vein and stratabound base metal sulfide mineralization of the Thermes ore-field, Rhodope Massif, NE Greece, is hosted in marbles. The Thermes area is a structurally complex, E-W-trending zone consisting of felsic gneisses alternating with amphibolites, amphibole-biotite, and biotite gneisses, and marbles. These rocks have undergone amphibolite facies metamorphism (5–7 kbar, 580°–620°C), in Upper Cretaceous to Eocene times, and were subsequently retrograded to greenschist facies metamorphism of Miocene age. Granitoids of Oligocene age, and volcanic rocks of Eocene-Oligocene age, crosscut the metamorphic rocks. Two major base metal sulfide ore varieties occur in the Thermes ore-field. The first comprises brecciated vein Pb-Zn mineralization, related to NNWand NNE-trending faults. The second comprises stratabound (manto) polymetallic, and Pb-Zn replacement ores with associated veins. On the basis of ore geochemistry, as well as field and textural evidence, these two ore varieties form part of a vein associated skarnreplacement base metal sulfide ore system. Based on fluid inclusion data in quartz, together with the iron content of sphalerites and existing lead and sulfur isotope data, it is suggested that after the cessation of the regional amphibolite facies metamorphism circulating evolved meteoric waters, probably with magmatic fluid contributions, deposited sulfide ores at temperatures of 200°2-400°C, and pressures of less than 300 bar. Ore was deposited as a result of increase in pH of the mineralizing fluids due to fluid-rock interaction, and adiabatic cooling and/or simple cooling accompanying fluid boiling. Thermochemical considerations indicate a pH increase from about 4 to 7 and a decrease in \(f_{S_2 } \) and \(f_{O_2 } \).

X‐Ray fluorescence analysis of base metal sulphide and iron–manganese oxide ore samples in fused glass disc

AbstractA procedure for the wavelength‐dispersive x‐ray fluorescence determination of major, minor and trace elements in fused discs of base metal sulphide ores and of iron–manganese oxide ores is described. The objective was to obtain reasonable chemical analyses of ore samples of a wide compositional range. Owing to the scarcity of well characterized geochemical reference ore samples, calibration was done with synthetic glass disc standards. The concentration range and the association of the elements considered in the standards take into account the geochemistry of most ore types. A fusion method with a high dilution ratio (sample‐to‐lithium tetraborate ratio= 1 : 10) was used to reduce the matrix effects. This allows a direct comparison of the synthetic standards with unknown geological sample discs. Two different methods of data reduction of the measured intensities were tested: (1) intensity‐based correction method for the determination of major, minor and trace elements and (2) peak/background ratio method for the determination of minor and trace elements. A critical evaluation of the reproducibility, as judged from duplicate analyses, and the accuracy, estimated by comparison with international reference materials, showed the procedure to be capable of obtaining reasonable chemical analyses for most elements of geological interest.

The design of an autoclave for studying hydrometallurgical reactions

An autoclave which may be used for studying hydrometallurgical reactions above 373 K and 1 atm is described. Its design is such that solid and/or liquid reactants may be added whenever desired. Portions of the reacting solution may be removed as required for analysis. The autoclave has been used to study the kinetics of the reactions between several aqueous solutions and metal sulphide ores. Results of a preliminary investigation between acidified copper sulphate and pentlandite are presented.

Relationship of stratabound ores with tectonic cycles of the phanerozoic and proterozoic

Abstract Comparison and analysis of certain stratabound Phanerozoic metal-sulfide ore deposits reveal a consistent and predictable association in time with tectonic settings and lithological assemblages corresponding with events of the Wilson Cycle This “cycle” of ore deposits, correlative with the cycle of tectonics and times of rifting, opening, closing, and assembly of Pangea, is also mirrored in events in and of the Phanerozoic ocean. Similar if not identical styles of extension and compression related tectonics and associated ores are reported in the Proterozoic, allowing a comparison of the Wilson Cycle ores with Wilson-like “ore cycles” present in the interval about 2.2 Ga to about 1.7 Ga and again in the interval about 0.9 Ga to about 0.6 Ga, the younger time overlapping with onset of Phanerozoic Atlantic tectonics. The Middle Proterozoic time of 1.7 Ga to about 1.0 Ga is represented by ores characteristic of rifting and sedimentation during a protracted period of apparent crustal warming and extension.

Precious metals in massive base metal sulfide deposits

Gold and silver are ubiquitous, sometimes minor but economically important metals in massive base metal sulfide ores. Their content, proportions and distribution in the ores depend on complex, interrelated factors of their source, mobilization, transport and deposition.

Trace element content of pyrites from Swedish ore types

Abstract Pyrites from Swedish base metal sulphide ores show trace element patterns characteristic for some types of ore. The indicative elements are Co and As. The use of these trace element patterns is proposed as a possible method for prospecting.

Molecular genetic studies on the thiobacilli and the development of improved biomining bacteria

AbstractAcidophilic autotrophic thiobacilli, which are able to oxidize metal and solubilize sulphide ores, are used industrially to leach metals from mineral ores. Genetic manipulation of the thiobacilli has the potential for the production of leaching bacteria with desirable characteristics for industry. In this review we examine the development of genetic systems in the thiobacilli and the present status of molecular genetics in the group.

Development and Economic Implications of Paleokarst, Molas Pass Area, Southwestern Colorado: ABSTRACT

With the emergence of the Mississippian Leadville Limestone, a climatically specific subaerial tower-karst surface developed in the Molas Pass area, with 80 ft of local relief. Much of this surface is buried under different thicknesses of the Early Pennsylvanian Molas Formation, in part a regolith of siltstone and residual clays from the limestone solution. Rising like small peaked knobs from a plain are three examples of the tower karst found near Molas Pass, the Molas Lake tower, Waterfall tower, and Sultan Creek tower. These illustrate the relatively low limestone solubility, strong fracturing, both joint and fault, and high water-table variations conducive to both tower and the related Kegelkarst formation. Folding may produce adverse conditions for the karst tending to hasten cavern integration and limestone removal. Tower karst and the predominance of kaolinite in the lower Molas, together with silica and hematite produced from soil ferralitization, suggest a subtropical to tropical climate with heavy rainfalls followed by rapid evaporation. The modern localization of this type of karst to areas below 30° of latitude implies a northward migration of the Molas Pass area since the Early Pennsylvanian. The complex stratigraphic relations between the fine-grained Leadville Limestone and the underlying Ouray dolomitic grainstone have made their field separation difficult and may indicate which areas were above and below sea level during the karst formation. This suggests a relative elevation of 100-200 ft for the Leadville at the time of the maximum tower-karst formation. The geologic controls on tower-karst development as observed in the Molas Pass area correlate well with the climate and geologic controls in a modern tower-karst analogue, central Jamaica. An understanding of the mechanisms of tower-karst formation and burial is directly applicable to petroleum stratigraphic trap location as in the Elk Basin field of northern Wyoming-southern Montana, and the localization of base metal sulfide ore deposits as at Gilman, Colorado. End_of_Article - Last_Page 915------------

A 'lattice-defect; free energy' approach to replacement processes in ore deposition

The probability is discussed of a close interrelationship between i) concentrations of lattice defects and associated free energy in minerals; and ii) solid state and chemical reactivity processes, in the formation of some ore deposits. The distributions of lattice defects and/or free energy near four base metal sulfide ore deposits, as indicated by thermoluminescence, are analyzed and the conclusion reached that lattice defects due to strain may have played a very significant part in pre-ore ground preparation and the localization of the ore zones. Defects caused by low-level radioactivity and some trace elements should have similar effects, but in one, if not all, of the cases examined they appear to have been of negligible importance. It is suggested that in cases where obvious structural or petrologic controls for the emplacement of ore deposits appear to be lacking, the controls may have been inconspicuous concentrations of either lattice defects or above normal free energy.

Power Requirements and Scale-up in Flotation

As part of a systematic programme for correlating mineral engineering process variables1,2, flotation machines are now being investigated. There is no need to stress the engineering importance of the flotation process. First applied more than fifty years ago for the recovery of fine sulphide minerals from Australian gravity plant tailings, to-day it is the only method for treating the major base metal sulphide ores, and is becoming of increasing importance for non-metallic ores and coal. As a mineral engineering operation, it is often second only to fine grinding in power consumption. Despite this, empiricism largely prevails from choice of equipment to control of process variables.

Nickel, cobalt, copper, zinc, lead and sulfur contents of some North American base-metal sulfide ores

Composites of mill feed from North American base metal sulfide mines have been analyzed for Co, Ni, Cu, Zn, Pb, and S. Co:Ni:Cu:Zn:Pb ratios and particularly Ni:Cu:Zn:Pb ratios show similar trends for igneous rocks and base metal sulfide ores, which are plotted on compositional diagrams. Similarities and one difference in trends for rocks and ores, and correlation of positions of rock and ore types, support a magmatic origin for these ores. Igneous rock types which are associated with these ores, show a distribution similar to that for North American igneous rocks, along a series of Cu-, Zn-, and Pb-rich ores.

Hastening the coloration of lemons

Several metal sulfide ore deposits (epithermal veins and skarn-type deposits) occur in the central east portion of Mexico (Sierra Madre Oriental). Historically, some of these deposits have been exploited since the 1500s and 1600s. Currently, there are millions of tons of mine waste materials with high content of potentially toxic heavy metals. This work focuses on geochemistry and mineralogy and modeling of redox and acid–base reactions of mine waste material from the Xichú mining area (Aurora Mine), Guanajuato state. The processed ore material at Xichú (circa 1 million tons) consisted of pyrite, arsenopyrite, galena, sphalerite, chalcopyrite, and minerals with Ag and some Au. The mine waste material contains considerable amounts of As, Fe, Pb, Zn, and Cu, in different mineral phases mostly, Fe-oxides and oxyhydroxides, sulfo-salts and traces of primary sulfides. Potential metal liberation and mobility pose a threat to the local population. Redox reactions locally produce pH around 2 in leachates with high metal content. Secondary mineralogy includes goethite, hematite, ferrihydrite, jarosite group minerals, gypsum and minor carbonates, among others. The geochemical dynamics is controlled by the seasonal rains (from June to September), along with high evaporation rates. These factors produce minor acid mine drainage and metal leaching. Redox and dissolution–precipitation reactions control the mobility of heavy metals into the surrounding environment. Arsenic and heavy metal content in tailings is up to 37% Fe, 62 gr/Kg of As, 2.4 gr/Kg of Cu, 13 gr/Kg of Zn and 17 gr/Kg of Pb. Sequential extraction experiments indicated that most of the As is bounded to Fe oxyhydroxides; Zn and Cu are mostly bounded to soluble phases and Pb is mostly bounded to sulfide. Mineralogical changes are controlled seasonally mainly by dissolution and precipitation of secondary phases: jarosite, gypsum, goethite and hematite and minor metal carbonates. Locally, some highly evaporated ponds have low pH (between 2 and 3) and very high concentrations of As and metals. The Geochemist's Workbench (Act2 module) software was used to model the redox conditions for the dissolution–precipitation reaction controlling liberation and mobility of As and metals into the environment. It seems that most of the As and metals are involved in a dissolution–precipitation cycle in the tailings piles and very few are released into the environment.