James R. Craig

Systematics of the spinel structure type

Systematic trends in the geometry of 149 oxide and 80 sulfide binary and ternary spinels have been examined from the standpoint of ionic radius and electronegativity. The mean ionic radii of the octahedral and tetrahedral cations, taken together, account for 96.9 and 90.5% of the variation in the unit cell parameter, a, of the oxides and sulfides, respectively, with the octahedral cation exerting by far the dominant influence in sulfides. The mean electronegativity of the octahedral cation exerts an additional, but small, influence on the cell edge of the sulfides. The equation a=(8/3√d)dtet+(8/3)doct, where dtet and doct are the tetrahedral and octahedral bond lengths obained from the sum of the ionic radii, accounts for 96.7 and 83.2% of the variation in a in the oxides and sulfides, respectively, again testifying to the applicability of the hard-sphere ionic model in the case of the spinel structure. Comparison of observed and calculated u values for 94 spinels indicates that up to 40% of the experimentally measured anion coordinates may be significantly in error. In addition to these compounds, u values are given for 52 spinels for which no data have previously been determined. Diagrams are presented for the rapid interpretation of the internal consistency of published data and the prediction of the structural parameters of hypothetical or partially studied spinels.

Cation ordering in the tetrahedral sites of the thiospinel FeIn2S4 (indite)

Abstract Recent X-ray and electron diffraction studies have substantiated earlier indications, based on dielectric behavior, e.s.r. studies, elastic constants, magnetic measurements, specific heat and spectral data, that in many cases the cubic spinel structure exhibits a small deviation from Fd3m symmetry. This discrepancy has been associated with a small displacement (less than 0.10A) of the octahedrally coordinated metal atom along [111] in space group F43m but has not hitherto been tested using precise single crystal X-ray diffraction data. Although more than thirtyhk0 reflections of the type h + k = 4n + 2, structurally forbidden for the space group Fd3m, are clearly visible in diffraction patterns from the thiospinel indite ( FeIn 2 S 4 ; a = 10.618(3) A ), a refinement in space group Fd3m using 412 unique X-ray data (u = 0.25907(7); inversion parameter = 0.947(7); R = 0.048) indicates that the structure may be satisfactorily described in terms of the conventional symmetry. A refinement of the data in space group F43m shows that the displacement, if present, is not detectable within experimental error but allows a rationalization of the observed diffraction symmetry in terms of an unequal distribution of In atoms over the two nonequivalent tetrahedral sites in F43m (100 and 83 ± 1% In, respectively) and the presence of a nonspherical distribution of residual electron density about the octahedral site.

Ore mineralogy of the Applachian-Caledonian stratabound sulfide deposits

Abstract The diverse ore mineralogies of more than 100 stratabound sulfide deposits that occur along the length of the Appalachian-Caledonian orogen have been tabulated. The minerals reflect the varying Cu:Zn:Pb ratios that have been used as a means to separate the ore deposits into six distinct types following the IGCP Project 60 guidelines. The ore deposits, each containing at least one million metric tons of ore, are typical of massive sulfide deposits throughout the world and provide a basis for contrasting and comparing this orogen with others. Differing grades of metamorphism have significantly modified the ore-mineral grain sizes and textures, but do not seem to have effectively influenced the number or variety of mineral species present.

Mercury pollution as a result of gold extraction in North Carolina, U.S.A.

Abstract Water, sediment and panned concentrate from active streams, together with some mosses and well waters, all from the vicinity of old Au operations in North Carolina, were analyzed to determine the extent of pollution from metallic Hg introduced into these areas in the 1800s and early 1900s and by modern “weekend panners”. Heavy mineral concentrates, Au grains, sediment and moss were all found to be indicators of Hg pollution, with concentrations of up to 784,000 μg/kg in heavy mineral concentrates, 7400 μg/kg in sediments, and 4900 μg/kg in moss. Surficial spots on Au grains contained as much as 44.8% Hg. Analyses of fish tissue from several of the drainage channels did not indicate Hg pollution with all values below the North Carolina average of 210 μg/kg. Mercury concentrations in stream and well waters were all below the LLD of 0.2 μg/l. In North Carolina, heavy mineral concentrates appear to be the best indicators of introduced metallic Hg.

Gold production history of the United States

Abstract Gold has played an important role in the settlement and economics of the United States. Commercial production from 24 states totaled more than 420 million troy ounces (13,000 metric tons) from 1804 through 1995. There were, no doubt, early undocumented discoveries by Native Americans, but the first records are those from the mid-1600s in the east and from the 1770s in the west. Commercial production began in 1804 in North Carolina and spread among several Appalachian states in the 1820s and 1830s as placer deposits were discovered and exploited. After peaking in the 1830s and 1840s, Appalachian production began to decline as deposits were worked out and as miners moved westward in response to the news of the discoveries in California in 1848. Appalachian production virtually ceased with the Civil War while production from California and adjacent states remained at several millions of ounces per year. As the California Gold Rush waned, new discoveries brought the Rocky Mountain states, South Dakota, and Alaska into prominence. Local, state and total production responded to time of discovery, extent of placers, labor availability, technology, government mandates and, of course, the price of gold. By 1900, the major gold rushes had occurred and most of the major producing districts were defined; however, the fixed price of gold (since 1837) provided a decreasingly attractive incentive for more exploration and exploitation. The rise in the price of gold, during the Depression provided a powerful incentive to increase gold production, but one that was cut short by War Production Board Order L-208 which closed the gold mines in 1942. In the post-war period, the fixed price, combined with the prohibition of American gold ownership, again proved to be a disincentive and gold production dropped. The era of free gold price that began in 1968, followed by the permission for Americans to again own gold, brought new interest in gold with prices rising briefly in 1980 to US

Compositional and textural variations of the major iron and base-metal sulphide minerals

850 per ounce and remaining above US

Halite and Hydrohalite from Lake Bonney, Taylor Valley, Antarctica

350 per ounce through 1995. This higher price, combined with the technology for bulk mining and processing of low grade ores, provided incentive for new exploration and exploitation. Consequently, gold production soared above 10 million ounces per year in the early 1990s with 65% coming from Nevada. There has been a general decrease in the grade of gold ores since the early 1900s and significant changes in the methods of recovery. Despite the decreasing grade, the reserves of recoverable gold have more than doubled since the early 1970s.

The inorganic geochemistry of coal, petroleum, and their gasification/combustion products

The crystal structures, stoichiometrics, electrical and magnetic properties, stabilities and mineral textures found in the metal sulphides are briefly reviewed. Eight of the major iron and base metal sulphide minerals, chosen because of their widespread occurrence (pyrite, pyrrhotite), role as the major ore mineral of a particular metal (chalcopyrite, sphalerite, galena, pentlandite), or importance as a carrier of rare or precious metals (arsenopyrite, tetrahedrite) are discussed in greater detail. The crystal structures and physical properties of these minerals are discussed, along with phase relations in the relevant sulphide systems. Particular emphasis is placed on the presentation of data on major and minor element compositional variations in these minerals and textural features commonly observed in ores containing them, both of which are of crucial importance in their metallurgical processing.

Tellurium and precious-metal ore minerals at Mina Capillitas, Northwestern Argentina

Halite (NaCl) and hydrohalite (NaCl·2H 2 O) have been found in the bottom sediments of Lake Bonney. These salts are in contact with the hypersaline bottom waters of the lake at depths below 28 m and occur with gypsum and calcite; a porous algal mat may be growing on at least a portion of the deposit. Hydrohalite formed during the coldest parts of the year is believed to be converted to halite during the slight warming during the austral summer. Thus, hydrohalite is only present on a year-to-year basis, whereas halite is preserved for long periods.

Mercury interactions in a simulated gold placer

Abstract The inorganic makeup of coal and petroleum differ in several crucial ways. The origins of these differences include the disparate geologic environments of formation, the contrasting parent materials (plant versus planktonic) and hence distinct organic species, and the physical state of the fuels (solid versus liquid). The inorganic chemistry of petroleum is usually controlled by the type and abundance of its organic compounds (i.e., V, Ni, ± Fe-bearing porphyrins and S-bearing thiols, sulfides, disulfides, thiophenic derivatives, resins, and asphaltenes), with significant, though often smaller contributions from entrained mineral phases. This near balance of inorganic compositional control causes petroleum to form combustion/gasification (pyrochemical) slag and ash with a large number of elements (i.e., V, Ni, S, Fe, Ca, Na, K, Mg, Si, and Al) in significant relative concentrations. This balance provides also opportunities for large departures from any given “norm”. The inorganic chemistry of coal, on the other hand, is dominantly controlled by its contained detrital and authigenic mineral matter, with relatively small contributions from organically carried elements other than sulfur. Detrital minerals are those that survive the geological processes of weathering and transport, and hence are a small group of physically resistant and chemically stable minerals including quartz, clay minerals, and oxides of Fe and Ti. The most abundant authigenic minerals in coal include clay minerals, pyrite/marcasite, carbonates, Ca- and Fe-sulfates, and Fe-oxides and hydroxides. Pyrochemical slag and ash from coal are therefore primarily enriched in Si, Al, Ca, Fe, and S. From a processing standpoint, the behavior of slag and fly ash is largely a function of the complexity of the fuels inorganic chemistry (including the original mode of occurrence of the various elements), and the observed oxygen fugacity. Pyrochemical environments vary from reducing to oxidizing as a result of proximity to the flame and operational mode (combustion versus gasification). Consequently, multivalent elements further contribute to the complexity of slag/ash behavior by essentially behaving as separately unique elements when in their various valence states. In coal, the two abundant, multivalent inorganic elements are Fe (0, + 2, and +3) and S (−2, 0, +2, +4, and +6). In petroleum there are four abundant, multivalent inorganic elements: Ni (0 or +2), Fe (0, +2, and +3), V (+2, +3, +4, and +5), and S (−2, 0, +2, +4, and +6). The larger number of abundant inorganic elements in petroleum than coal, as well as the broader range of associated valence states, leads to more diverse slag/ash species formed during petroleum combustion/gasification, and consequently less predictable slag/ash behavior. A phase characterization of slags produced by the gasification of petroleum coke (a petroleum refining byproduct) illustrates their increased complexity with respect to typical coal slags.