Ore Section Research Articles

REE and their relevance to the development of the Kupferschiefer copper deposit in Poland

Over one hundred samples, representing mainly clayey-organic- and carbonate-rich shales (Kupferschiefer) but also other members of different ore sections, including hangingwall dolomites (Z1 Werra) and footwall Weissliegend sandstone (Lower Permian), have been collected in different mines of the Lubin–Głogów mining district, mainly near the contact (transitional zone) between the copper-mineralized zone and secondarily oxidized (Rote Fäule=RF) zone. In general, the Polish Kupferschiefer shales are enriched in MREE in comparison to NASC. In a typical copper-rich ore section the REE amounts and patterns depend on lithologies, being generally similar in shales and dolomite. ∑REE vary among sandstones, shales and dolomites (average 73, 143 and 85ppm, respectively), probably reflecting mainly their clay contents. Sandstones have strongly convex REE patterns with positive Eu and negative Gd anomalies and depletion in LREE and enrichment in MREE relative to HREE. The REE patterns of shale and dolomite are similar to one another and rather flat, with strong negative Eu anomalies, and a small positive Gd anomaly in the case of shales.The REE patterns of shales from the mineralized Cu-zone are generally convex (MREE enriched) and have negative Eu anomalies. However, in a section with Cu-, Zn- and Pb-shales the REE pattern of Pb-bearing shales shows a positive Eu anomaly, in contrast to other shales and overlying dolomite. More oxidizing conditions of deposition can be assumed for Pb-shales.No significant differences between REE distributions in transitional and oxidized zones have been observed. Their REE patterns are more convex and are much higher (av. 247ppm) than those in the mineralized zone and they do not show Eu anomalies. The strongly convex pattern may suggest either enrichment in MREE or relative depletion in LREE due to localized precipitation of light REE minerals, both in shales and in the uppermost part of the sandstones.Two unique sections, one Cu-rich and one Cu-lean (partly oxidized), comprising three shale beds interbedded with dolomites have been compared. Generally ∑REE contents are similar in these two sections. Also similar are changes in contents of REE between beds in both sections, which decrease significantly upwards (from 157–171ppm to 54–60ppm). The REE patterns of the lowermost beds (directly overlying sandstones) are ramp-like, with LREE enrichments. The upper beds have concave REE patterns. Comparison between sections shows generally stronger negative Eu and positive Gd anomalies in the highly-mineralized section.There is a highly significant positive relationship between Cu and ∑REE contents in Cu-rich shales and slightly less significant negative relationship for their concentration in oxidized and transitional shales. There is a moderate significant positive correlation between P2O5 and ∑REE contents in Cu-rich shales.The observed differences in REE contents cannot be provenance dependent but have been caused by diagenetic processes, possibly related to mineralization and oxidation processes. Europium anomalies, generally reflecting different Eh conditions in the deposit, can be eliminated by the prolonged oxidation. Strong enrichment of the RF zones in REE may result from their desorption from large volumes of oxidizing, including mineralizing, solutions which probably emerged from the underlying molasse lithologies into the Rote Fäule areas. Higher contents of REE in the lowermost shales suggest upward movement of solutions from the underlying sandstones also far away from the RF areas.

Investigation and in situ visualisation of interfacial interactions of thermophilic microorganisms with metal-sulphides in a simulated heap environment

This study sought to provide a better understanding of the dynamics of microbial-metal sulphide interfacial processes relevant to heap bioleaching. Attachment and subsequent biofilm formation by Metallosphaera hakonensis (M. hakonensis) on the surface of massive chalcopyrite and pyrite samples, as well as a low-grade chalcopyritic whole ore were investigated. The method made use of a biofilm reactor in which thin sections of mineral ore were mounted. Operating conditions in the reactor simulated those of a bioheap in terms of fluid-flow and mineralogy, where the low-grade chalcopyrite ore sections were used. Pure cultures of M. hakonensis were used to inoculate the reactors and the attachment and subsequent biofilm development visualised in situ after 2, 4 and 8 days using a combination of atomic force and epifluorescent microscopy (AFM–EFM) as well as confocal scanning laser microscopy (CSLM). This revealed insights into biofilm structure and architecture. The effect of varying temperature on the extent of attachment and biofilm development was also assessed after 4 days using three temperature regimes: room temperature (20±1°C), 45°C and 65°C. The density of the attached micro–colonies increased with an increase in time, indicative of an actively growing biofilm. The extent of surface coverage and proliferation of the biofilm was dependent on the temperature, with surface coverage being more extensive at 65°C, near the optimal temperature for growth. Preferential attachment and biofilm formation to sulphide minerals was observed, with increased surface coverage of pyrite mineral surfaces relative to chalcopyrite and low-grade ore. The AFM–EFM technique enhanced the level of detail at which site specific associations of microorganisms with mineral surfaces could be assessed. Spatial orientation and density of attached micro-colonies were noted.

Simulation Study on the Stability of Mining Thin Flat-Grade Iron Ore Body with Hydraulic Support Longwall Method

This paper proposed hydraulic support longwall method for mining glacis thin orebody. The DaZhuang ore section of Guandian Ore Mining whose orebody in the line of -8＇—-16＇was chosen as the research object. It applied the FLAC numerical simulation method to study the changes of surrounding rock stress in the mining face, displacement and plastic zones, and put forward the changing law of the rock stress, displacement and plastic zones in the mining process. Besides, it proved that the mechanical condition of the roofs changed in different stages. When the distance between pillar and mining face was in the range of 4m—8m, the state was relatively stable, and the pillar and surrounding rocks were in small range of shearing and tensile yield. When distance was 12m, the roof suffered from compression. When it was up to 16m, the roof and bottom rock displayed tension. However，the appreciation of stress changed very little at different stages. The stress concentration circle formed between the top and bottom of the pillar, and the unloading appeared in the top and bottom gap. The nearer to the coal face, the more powerful of stress concentration, and the influence of pillar’s position on stress concentration degree is very little in the front of coal face. The structure would be in stable equilibrium when the distance between single stent and coal face is 12m. In such circumstances, the security of roof would be improved if more stents are added

In situ investigation and visualisation of microbial attachment and colonisation in a heap bioleach environment: The novel biofilm reactor

In this paper, the development of a novel means of investigating the attachment and subsequent biofilm formation of mineral bioleaching micro-organisms to mineral surfaces in situ is described. The protocol was developed to investigate the interactions of micro-organisms with sulfide minerals and low-grade chalcopyrite ore under conditions resemblant of a bioheap environment. The method makes use of a biofilm reactor in which thin sections of mineral ore are mounted. The reactor is operated as a continuous flow-through system. Attachment of pure and mixed cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum is assessed. The technique allows for the investigation of microbial ecology with special regard to microbe–mineral attachment, site and mineral specific associations of micro-organisms and spatial organisation of microbial communities present through the use of fluorescent microscopy techniques. Preliminary fluorescent in situ hybridisation (FISH) analysis of the attachment of L. ferriphilum and A. ferrooxidans to massive chalcopyrite sections, as well as to low-grade chalcopyrite containing ore sections is presented. In the case of both low-grade and massive sulfide mineral samples, attachment of mixed micro-colonies was observed in regions where surface defects were prevalent. In low-grade samples, preferential attachment was observed in regions where sulfide minerals were present. The density of the attached micro-colonies increased with an increase in contacting time (from 20, 72 and 96 h) and was indicative of an actively growing mono-layered biofilm.

Interaction of microfractures: The mechanism of network building

Microscopic study of fractures in polished sections of Precambrian metamorphic sulphide ore reveals that distinct crack morphologies such as dimensions, orientation, shape and distribution are controlled by mineral associations and temperature conditions during failure. Microfractures developed in a regime of low differential stress where hydraulic pressure triggered the episodic crack opening by pressurized fluids. Fracture arrays consist of segments of varied orientation and width resulting from initially isolated cracks. Linear geometry of fracture systems is complicated by interaction of their segments. Three distinguished types of interaction include in-line propagation of two cracks tip-to-tip (type 1), propagation of two cracks along curved paths towards each other (type 2) and propagation of single crack obliquely towards the other crack (type 3). Different interaction types result from variation in fracture spacing and relative position of their tips and distinguished by the angle of propagation. The ratio of overlap/spacing for interacting fractures is negative (− 0.25 to 0) for type 1 interaction and positive for type 2 (0 to 45), and type 3 (0 to 15) interactions. The mean value of the angle of fracture propagation in the onset of the interaction is obtained as 12° for type 1, 25° for type 2 and 38° for type 3 interactions. The mean value of the angle of fracture propagation accommodating linkage is 4° for type 1, 36° for type 2 and 12° for type 3 interactions. The initial crack distribution is crucial in determining whether their coalescence occurs resulting in mature fracture networks.

Mineralogical and geochemical zoning and genesis of massive sulfide ores at the Oktyabr’sky deposit

Fractional crystallization and emanation differentiation of sulfide magma and related mineralogical and geochemical zoning are exemplified in massive sulfide ores of the Oktyabr’sky deposit, Noril’sk district. The mineralogical zoning is expressed in the change of mineral types of ore from pyrrhotite (Po) to chalcopyrite (Cp) (from the flanks to the center of the ore lode). In terms of geochemistry, the Cu content, Cu/(Cu + Ni) ratio, and contents of noble metals incompatible with Mss (Pt, Pd, and Au) increase in this direction, while the S and Fe contents decrease. The distribution of elements compatible with Mss (Ir, Os, Rh, and Ru) is more complex. Their contents decrease from Po to high-Cu Cp ore, although there is a second maximum for Cb-type ore. The distribution of ore elements in the vertical and horizontal sections of massive ores at the deposit is different. The upper outer contact zone and frontal parts of massive ore lodes are enriched in all ore elements and a light sulfur isotope. The succession of enrichment is correlated with the relative affinity for sulfur and remains independent of the affinity of these elements for Mss (Pd-Rh, Os-Au). The possible role of liquid immiscibility of sulfide magma in the development of the mineralogical and geochemical zoning of massive ore is discussed.

Microscopic digital image analysis of gold ores: a critical test of methodology, comparing reflected light and electron microscopy

Automatic digital phase imaging should yield unbiased and representative characterizations of gold ores. However, this is not a simple task due to low gold grade, fine grain size, possible complex mineralogy, nugget effect, etc. Using the same sections of a gold-rich ore, a critical test was performed using an optical microscope (OM) and an electron microscope (EM). In general, the two methods are consistent and useful for ore processing. There are some minor differences, such as the detection of very fine gold grains is enhanced by EM.

Age and thermal history of the east ore section, Bayan Obo Deposit—a fission track study

Considerable attention has been paid in recent years to the study of geothermal history by using spontaneous fission tracks of238U recorded in minerals. Apatite and zircon were used for fission track study in this paper because apatite has been widely used as a natural geothermometer (Wang Shicheng et al., 1994) to reveal the thermal evolution of sedimentary rocks based on its low annealing temperature of fission tracks and zircon is characterized by a closing temperature above 700°C. The samples were collected from ferruginous, siliceous slate wall rock at the upper levels of the orebody and Nb-REE-Fe ores from deep tunnels. The age and thermal evolution of the orebody were discussed in terms of fission track characters and their length variations observed in the coexisting apatite and zircon in the same specimen.

Bacterial and chemical leaching pattern on copper ores of sandstone and limestone type

Thin polished sections of copper sulphide ore were placed as an energy source in stationary cultures of wild strains and Thiobacillus neapolitanus at pH 7.5. Scanning electron microscopy revealed characteristic leaching patterns that depended on the type of leaching process and time of bioleaching. In some cases, a biological film on the ore surface was observed. Close contact between bacterial cells and ore seems necessary for leaching in some cases.

Deformation textures in pyrite from the Vangorda Pb-Zn-Ag deposit, Yukon, Canada

AbstractThe Vangorda Pb-Zn-Ag orebody is a 7.1 M tonne, polydeformed stratiform massive sulphide deposit in the Anvil mining district, Yukon, Canada. Five sulphide lithofacies have been identified within the desposit with a typical mineralogy of pyrite, sphalerite, galena, and barite. Pyrrhotite-sphaleritemagnetite assembalges are locally developed. Etched polished sections of massive pyrite ores display relict primary depositional pyrite textures such as colloform growth zoning and spheroidal/framboidal features. A wide variety of brittle deformation, ductile deformation, and annealing textures have been identified. Brittle deformation textures include thin zones of intense cataclasis, grain indentation and axial cracking, and grain boundary sliding features. Ductile deformation textures include strong preferred grain shape orientations, dislocation textures, grain boundary migration, dynamic recrystallisation and pressure solution textures. Post deformational annealing has produced grain growth with lobate grain boundaries, 120° triple junctions and idioblastic pyrite porphyroblasts. The distribution of deformation textures within the Vangorda orebody suggests strong strain partitioning along fold limbs and fault/shear zones, it is postulated that focussed fluid flow in these zones had significant effects on the deformation of these pyritic ores.

Sedimentation Associated with Cirque Barite-Zinc-Lead Deposit: ABSTRACT

The barite-zinc-lead Cirque Deposit and other major showings in the Gataga district are part of an Upper Devonian to Mississippian sequence of basinal shales and submarine fan deposits of chert pebble conglomerate which were derived from the northwest. This sequence is preserved in the Akie, Pesika, and Gataga troughs, and unconformably overlies Ordovician to Silurian slope and basinal facies of the Kechika trough. The Akie trough is host to all known potentially economic barite-zinc-lead deposits in the district. Both regional and detailed linear elements of the Cirque Deposit trend northwesterly and are asymmetric normal to the strike line. The background depositional unit is a soft gray aluminous shale which grades into black and carbonaceous shale to the southwest. An envelope consisting of diagenetically silicified fine carbonaceous clastic units was formed about the deposit. The outermost part of the diagenetic envelope consists of ribbon-bedded porcellanite with blebby and laminated massive barite on the northeast. Silicified platy poker chip shales with calcareous siltstone laminae are between the ribbon porcellanites and ore. The core of the cycle consists of up to 70 m of barite and sulfides on the axis of the deposit. Laterally, the ore section interfingers to the northeast with an e ual thickness of flaggy to blocky bedded silicified black shale containing abundant finely laminated pyrite. Pb:Zn ratios increase northeasterly, and ore isopachs are asymmetric toward the northeast with the thickest zone being on the southwest edge of the deposit. End_Page 585------------------------------ Genetically the barite-sulfide accumulations are considered to result from exhalative activity restricted to regionally developed basement faults. Accumulation occurred within a minor trough with resultant facies asymmetries being related to different topographic and paleochemical conditions during sedimentation and diagenesis. End_of_Article - Last_Page 586------------

Precious metals in volcanic peridotite-associated nickel sulfide deposits in Western Australia; II, Distribution within the ores and host rocks at Kambalda

A detailed study of the distribution of Pd, Ir, and Au in the sulfide component of contact ore layers at Lunnon shoot has shown consistent differences between the matrix and massive layers and significant lateral variation within them. Palladium values in sulfides increase upward in ore sections, and when average values are compared with those predicted by the relationship between Pd and Ni in mined ore (Ross and Keays, 1979), loss of Pd is indicated. The Pd-Au-Cu-enriched footwall sulfide stringers are believed to be the principal repository of remobilized Pd. Iridium has a more uniform distribution and there is no evidence of important loss or gain from contact ore, even though massive layer sulfides contain more Ir at nearly all sample locations. Average values of Au are higher in matrix layer sulfides and some loss of Au from contact ore into footwall stringers, and perhaps more distant sites, is likely. If it is assumed that the distribution of these metals, and of Ni and Cu, was uniform during emplacement of sulfide melt, their present distribution can be attributed to the following processes. Redistribution of Ir could have occurred during igneous cooling in the presence of a high thermal gradient at the base of the komatiitic volcanic pile and could have been accompanied by some movement of Pd in areas of active stress. Most redistribution of Pd is attributed to stress during the existence of metamorphic monosulfide solid solution, and significant redistribution of Cu may also have been induced by stress. The circulation of latestage sulfur-bearing solutions through contact ore layers (Seccombe et al., 1981) could have transferred Pd, Au, and Cu from contact sulfides (particularly from the more permeable massive layer) to footwall stringers and resulted in the close association of anomalous values of Au and Cu. Transfer of about 5 percent of the S in the matrix layer to the massive layer by these solutions would account for the consistently higher Ni content of the matrix layer and development of secondary pyrite in the massive layer.Analyses of sulfide mineral separates from several shoots have consistently shown that pentlandite is the dominant host for Pd; Ir is more uniformly distributed with higher values in pyrite; and chalcopyrite (and perhaps pyrite) is the most important host for Au. Concentrates of secondary pyrite appear to have normal values, which suggests some movement of Ir during its development. The precious metals appear to be uniformly distributed through sulfide mineral hosts, but observed variation in ore sections and layers requires that their abundance in the preferred sulfide host must vary considerably.Further work has strengthened the conclusion of Ross and Keays (1979) that olivine in the original komatiitic magmas was the principal host for Ir and the liquid component was the principal host for Pd. Olivine control lines for Pd and Ir in primary melts predict values at lower MgO in good agreement with those in hanging-wall basalts at Kambalda. At higher MgO they agree closely with the most recent estimate for pyrolite and a chondritic Pd:Ir ratio of about unity. These predicted values result in a substantial increase in Pd:Ir with decreasing MgO. Results from Kambalda and other Ni sulfide deposits indicate that the Pd:Ir ratio of the sulfide melt may approximate that of the coexisting silicate melt even though absolute values may vary widely. This variation exceeds that expected from the relative volumes of silicate and sulfide melt and may result from differences in factors such as f (sub s 2 ) and f (sub o 2 ) when immiscible sulfides formed. Measurements of Pd and Ir offer scope for defining the MgO contents of primary silicate melts associated with immiscible sulfides and may allow a more precise definition of f (sub s 2 ) (and perhaps f (sub o 2 ) ) during formation of immiscible sulfide melts.

Sulfide paragenesis and sulfur mobility in Fe-Ni-Cu sulfide ores at Lunnon and Juan Main shoots, Kambalda; textural and sulfur isotopic evidence

Sulfur isotope data from a range of ore types at Lunnon and Juan Main shoots, Kambalda, have been determined in an attempt to constrain models for the crystallization of the sulfide ores. The place of pyrite in the sequence of ore formation and modification is evaluated from data representing the widest possible range of pyrite types showing variable textural relations to coexisting pyrrhotite.The sulfur isotopic distribution (68 mineral analyses) yields a mean value of 2.4 per mil (range -0.5 to +3.8%; standard deviation + or - 0.8%). The distribution is characterized by a small spread in values and isotopic disequilibria between coexisting minerals. There is no statistical difference between pyrrhotites in massive ores and matrix ores at Lunnon shoot and no systematic variation in isotopic composition of pyrrhotite and sparse pyrite in a single ore section from the same deposit. These data are consistent with previous suggestions that massive and matrix ores crystallized independently at the magmatic stage. Variable but overall less positive delta 34 S values for sulfides from disseminated ores from Lunnon shoot are consistent with control of isotopic compositions by Fe-related redox mechanisms during alteration of the ultramafic hosts.The delta 34 S values of pyrite and pyrrhotite from massive ores at Lunnon and Juan Main shoots are indistinguishable and the origin of coarse-grained pyrite remains equivocal despite the isotopic data. The data are, however, consistent with derivation of fine-grained pyrite by late-stage, relatively low temperature, sulfurization processes as suggested by textural studies. The greater permeability of the massive ore, relative to more disseminated ores and barren ultramafics, due to thermal contraction following magmatic and/or metamorphic cooling, is considered the controlling factor.The secondary nature of a significant proportion of the pyrite in massive ores severely limits attempts to use present bulk compositions to predict magmatic crystallization sequences within ore and the use of sulfur/metal ratios to estimate parameters such as f (sub o 2 ) at the magmatic stage.

Economic geology of the Mishraq native sulfur deposit, northern Iraq

The Mishraq native sulfur deposit is in northern Iraq about 40 km southeast of Mosul and 315 km north of Baghdad. This deposit is the largest known occurrence of stratiform bioepigenetic sulfur, containing at least 100 million tons of elemental sulfur. It underlies a 10 km 2 portion of the southeast end of a northwest-trending, doubly plunging anticline on the west bank of the Tigris River at its confluence with the Great Zab River. The deposit is in one anticline among many in the folded portion of the Mesopotamian depression and represents part of what may be the largest reserve of elemental sulfur in the world.Small, tight, en echelon folds are superimposed on the southwest limb of the Mishraq anticline with axial trends similar to the main fold (320 degrees ). Faulting is normal and reverse with dominant northwest and subordinate northeast trends. Mining-induced subsidence of 4 to 5 m causes fractures which tend to follow these preexisting directions.The sulfur mineralization is in three main zones of vuggy and bituminous bioepigenetic limestone in the basal Lower Fars Formation of middle Miocene age and marine origin. The Lower Fars consists of intercalated bituminous marine carbonates (dolomite, limestone, marl) and anhydrite/gypsum with minor shale and sandstone interbeds. The depositional environment was of periodic marine influxes followed by evaporation in a partially barred basin with southern access to the sea.The sulfur forms by oxidation of hydrogen sulfide produced during metabolysis of petroleum and anhydrite/gypsum by anaerobic bacteria (D. desulfuricans), a conclusion supported by the 34 S and 13 C fractionation data. Sulfur mineralization is thickest in areas of intense folding and faulting which enhance solution, movement, and mixing of reactants. Combined thickness of the three sulfur-bearing zones is from 2 to 123.9 m, with a maximum ore section of 107.9 m and a grade of 23.14 wt percent sulfur. Seven ore types have been recognized of which predominant coarse crystalline sulfur alternates with bands of secondary limestone.Hydrologic conditions at the mine are complex with subsurface drainage via karst features, fractures, faults, and vuggy porosity within the ore zones of the productive member. The productive member contains the bulk of the ground water, although up to 13 aquifers have been recognized throughout the section, and it is intersected by the Tigris River. A very steep hydraulic gradient exists with flow southeastward toward the Tigris where it is discharged from springs in and beside the river. Hydrogen sulfide-carbonate waters predominate. Recharge is mainly at the northwest portion of the anticline where the Lower Fars crops out. The ground water connection and flow to the river is important in sulfur generation as it is the pathway by which oxygen is carried into contact with hydrogen sulfide at depth yielding sulfur and water.The deposit is currently being mined by the Polish hydrodynamic (modified Frasch) process at a rate of about 600,000 tons per annum out of a total capacity of 1,000,000 tons per annum. The maximum capacity has not been reached because of infrastructural constraints related to transportation and because the mine is difficult to operate. Large injection water losses and excessive bitumen contamination are paramount. Water losses are mitigated by the installation of subsurface impermeable screens. Bentonite/sulfuric acid filtration removes the excess bitumen but at a cost of 8 to 25 percent loss of sulfur in filter cake and skim foam.Initially sulfur was vatted at the mine, crushed, and shipped via rail to the port of Um Qasr about 1,000 km south of Mishraq. Liquid sulfur is currently shipped to the port where vatting is done as necessary.

Self potentials at the Joma pyrite deposit, Norway

SP-patterns both in drill holes and at the surface are separated into two parts: 1. (1) a general trend indicating the dipole pattern in the country rock around the deposit with maximum potential variations approximately 200 mV; and 2. (2) alternating potentials, with minima down to −800 mV in the massive sulphides, the steep gradients of which indicate EMF's at the country-rock/sulphide interfaces. Sulphides and country rock are supposed to constitute galvanic cells of which the sulphides represent dipole electrodes, and the pore water of the country rock the electrolyte. The redox potential of the pore water decreases with depth. Separation of the SP potential pattern into two dipole systems offers possibilities for: 1. (1) locating possible extentions of ore bodies with depth; li(2) rough estimations of tonnage of total ore bodies if the tonnage of upper parts are known; and 2. (3) estimations of sulphide contents of ore sections without analyzing drill cores or drilling cuts. The concept of the galvanic cell indicates that electrochemical processes to some extent control the dispersion of chemical elements around ore deposits.

Die Messung des Winkels der Minimal-Intensit�t der Reflexion in der Auflichtmikroskopie von opaken Substanzen, insbesondere von Erzmineralen

By the aid of a goniometer with the optic of a microscope it is possible to measure well reproducible the principal angle of incidence of a polished ore section. It may be used as a standard material constant for identifications. By the use of objective methods, with the aid of photomultiplier tubes and analysis by computation an accuracy of some few minutes of arc is within reach. Whereby certainly the quality of the sections and the polishing have to satisfy high requirements. The measurements are done without using a standard of comparison. They may be used as complement to the common measurements by vertical illumination. Details of the object are measurable down to a minimum diameter of about 15 μm.

Barren halite bodies in the sylvinite mining zone at Esterhazy, Saskatchewan

The potash-rich sylvinite zone mined at Esterhazy, Saskatchewan, contains irregular bodies of halite referred to as salt horses. Cuts through the salt horses range from less than 20 sq. ft to more than 200 sq. ft. Contacts between salt horses and the enclosing ore beds are normally irregular but well defined.There is significantly more bromide in both halite and sylvite in the salt horses (mean bromide 102 ppm and 1470 ppm respectively) than in adjacent ore beds (mean bromide 81 ppm and 1020 ppm respectively) although bromide contours within a horse bear little relationship to the geometric form of the horse.Rubidium in sylvite, unlike bromide, is not significantly different in the ore beds and salt horses (mean rubidium 37 ppm and 33 ppm respectively).Details of stratification, principally layers of clay–carbonate, can be traced from normal ore sections through the smaller salt horses. This suggests that the horses formed either contemporaneously with the ore beds or by later modification of the ore beds, without complete destruction of primary layering.It is suggested that the salt horses were formed by localized leaching of sylvite from the ore beds by brines saturated in sodium chloride. Some halite would be precipitated as sylvite dissolved. Prior to leaching, residual brines associated with the ore beds, capable of precipitating sylvite containing 1300 ppm bromide (near the upper range of bromide in sylvite of the ore beds), would be saturated in sodium chloride and potassium chloride. Up to 30% dilution of these residual brines with sodium chloride saturated brines (formed by the dissolution of halite) would produce brines which, in contact with the ore section, would dissolve sylvite and simultaneously precipitate halite. The resulting halite would contain about the same amount of bromide as the halite in the salt horses.No significant change in bromide or rubidium could be detected in the ore beds as a salt horse is approached. It is therefore unlikely that these trace elements can be used to predict the proximity of a salt horse during mine development. However, the higher bromide of the salt horses provides a possible means to differentiate, in drill core, between a barren hole due to a salt horse and a barren hole due to non-deposition, or erosion, of an ore zone.

Variation in Etch Behaviour of Jacobsite with Different Cell Dimensions

DURING the study of polished sections of manganese ores from the Kodur Group of mines, Srikakulam Dt., Andhra Pradesh, India, I came across three different types of jacobsite, associated with other manganese minerals like braunite, hausmannite, pyrolusite, cryptomelane, coronadite and γ-MnO2. It is the interesting variation in the colour and etch behaviour in the different types of jacobsite that attracted my attention, and investigations to find out the cause of such variation were attempted.

A procedure for polishing ore sections with diamond abrasive

A procedure for polishing ore sections with diamond abrasive

A method for polishing sections of ores

The procedure starts with rough ground specimen. Grinding is in two stages on iron laps designed to maintain a flat surface as the lap wears. Polishing is done on a lead lap. The construction and operation of the machines are described and grades of abrasives and special mixtures of oils are given. Grinding and polishing can be done with specimen held in the hand. A supplementary device holding a mounted specimen mechanically permits high pressure for polishing and greatly reduces polishing time for hard materials. The grinding methods are effective in making thin sections.