Aspects of the supergene geochemistry of copper, nickel and bismuth

The solution geochemical conditions associated with the development of supergene copper mineralisation in the E22, E26 and E27 deposits at Northparkes, New South Wales, have been explored. Determination of a stability constant for sampleite [NaCaCu5(PO4)4Cl·5H2O], a conspicuous species in the upper oxidised zone of E26, has led to an understanding of the differences between the three deposits in terms of the influence of groundwater geochemistry on their mineralogical diversity. Modelling of copper dispersion from the three deposits using current ground water compositions as proxies for past solution conditions has shown that the elevated chloride concentrations associated with E26 have negligible influence on total dissolved copper concentrations over a wide pH range. The results are discussed with respect to applications in exploration geochemistry for the discovery of new ore deposits in the region. Determination of a stability constant for lavendulan [NaCaCu5(AsO4)4Cl·5H2O], the arsenate isomorph of sampleite, suggests that solid solution between lavendulan and sampleite is likely to be extensive and this has been established by reference to mineral compositions from a number of deposits. Activity-activity phase diagrams have been developed to explain the common mineral associates of lavendulan and differences between the analogous phosphate and arsenate systems. With respect to the occurrence of lavendulan in the oxidised zone of the Widgiemooltha 132 N ore body, Western Australia, its crystal chemistry explains why Ni does not substitute for Cu in the lattice. This is despite Ni being abundantly available in the deposit and substituting freely into other copper-based minerals. The substitution of Ni for Cu was explored in a study of supposedly Ni-rich paratacamite, Cu2Cl(OH)3, from the deposit. It transpires that much of this is a new mineral, gillardite, Cu3NiCl(OH)6, the isomorph of herbertsmithite, Cu3ZnCl(OH)6. The nature of gillardite was thoroughly investigated and the mineral was approved as a new species by the International Mineralogical Association. A high resolution single-crystal X-ray structure of gillardite has been completed. In addition, the substitution of Ni in simple carbonate lattices has been explored as gaspéite, NiCO3, Ni-rich magnesite, MgCO3, and calcite, CaCO3, are all common species in the oxidised zone of the Widgiemooltha 132 N deposit. Attention was subsequently focussed on the geochemistry of the element Bi, with special reference to deposits of the Kingsgate region, New South Wales. This study has led to a modern assessment of the Mo-Bi deposits in the area and new Bi sulfosalts from the Wolfram pipe at Kingsgate are described. A survey of secondary Bi minerals from a host of deposits has led to the development of a model for the dispersion of Bi in the supergene environment, which will have widespread applications in exploration geochemistry where Bi is used as a pathfinder element. Calculations of aqueous Bi species in equilibrium with bismite, Bi2O3, bismoclite, BiOCl, and bismutite, Bi2O2CO3, over a wide pH range show that the element is very insoluble under ambient oxidising conditions. It is noted that the results of previous geochemical exploration campaigns in the region will have to be reassessed

Infrared Spectroscopic Study of Natural Hydrotalcites Carrboydite and Hydrohonessite

Infrared spectroscopy has proven most useful for the study of anions in the interlayer of natural hydrotalcites. A suite of naturally occurring hydrotalcites including carrboydite, hydrohonessite, reevesite, motukoreaite and takovite were analysed. Variation in the hydroxyl stretching region was observed and the band profile is a continuum of states resulting from the OH stretching of the hydroxyl and water units. Infrared spectroscopy identifies some isomorphic substitution of sulphate for carbonate through an anion exchange mechanism for the minerals carrboydite and hydrohonessite. The infrared spectra of the CO3 and SO4 stretching region of takovite is complex because of band overlap. For this mineral some sulphate has replaced the carbonate in the structure. In the spectra of takovites, a band is observed at 1346 cm−1 and is attributed to the carbonate anion hydrogen bonded to water in the interlayer. Infrared spectroscopy has proven most useful for the study of the interlayer structure of these natural hydrotalcites

Gaspéite-magnesite solid solutions and their significance

It is a surprising fact that, despite the increasing number of secondary minerals of Ni(II) recognized from oxidized base metal deposits (Anthony et al. 2003), the supergene chemistry responsible for their formation remains poorly understood. An understanding of this chemistry would be desirable in view of its importance with respect to geochemical exploration for the element, its behaviour in the regolith and the potential development of commercially exploitable secondary nickel resources. Of the secondary nickel minerals known, gaspéite, NiCO3, is perhaps the most common and has been observed in a number of Western Australian deposits

Chemical mineralogy of the oxidized zones of the E22, E26 and E27 ore bodies at Northparkes, New South Wales

A number of porphyry copper-gold deposits at Northparkes in central New South Wales are associated with finger-like intrusions of 430-440 Ma quartz-monzonite porphyries, which intrude Ordovician age Goonumbla volcanics (Heithersay et al. 1990). Major primary minerals are pyrite, bornite and chalcopyrite, together with economically significant native gold. Both primary and secondary ore from three bodies, E22, E27 and E26 North (E26) have been worked for copper and gold since 1994. The three deposits are covered by a mixture of clays, some of which are in situ weathering products, and transported overburden (Arundell 2004, Heithersay et al. 1990). The region has experienced prolonged and episodic weathering. Two significant weathering events have been identified, one in the Carboniferous and a subsequent event in the Cenozoic (O'Sullivan et al. 2000, Pillans et al. 1999). As a result, the E22, E26 and E27 deposits display well-developed oxidized zones, with intense leaching of the upper sections (Crane et al. 1998, McLean et al. 2004). The base of oxidation extends to 80 m from surface, with strong kaolinization from approximately 5 to 45 m below surface. Upper oxidized zones are dominated by the secondary Cu(II) phosphate minerals libethenite (Cu2P040H) and pseudomalachite (CU5(P04)2(OH)4) and, uniquely to E26, sampleite (NaCaCu5(P04)4C1.5H20). Beneath the phosphates a zone dominated by malachite (CU2C03(OH)2), azurite (CU3(C03)2(OH)2) and chrysocolla (CuSi03.nH20) gives way at depth to a thin native copper-cuprite (Cu20)-chalcocite (CU2S) supergene enriched zone. E26 is exceptional in that the formation of the secondary Cu(II) carbonates was preceded by extensive precipitation of atacamite (Cu2CI(OH)3), this being reflected by the compositions of present ground waters (McLean et al. 2004); those associated with E26 are much more saline (NaCI). We have reconstructed the solution conditions associated with the development of these assemblages to better understand the dispersion of copper. In order to model the environment of phosphate mineral deposition in E26 a stability constant for sampleite at 298K has been measured

The 'lost' mines of Kingsgate, New South Wales

Some 30 'Kingsgate'-style quartz pipes, some of which carry Mo and Bi mineralization, are known to the immediate south of the Yarrow River but separate from the main Kingsgate mining field in New South Wales. Mining in the area commenced around the same time as at Kingsgate, but the deposits have been largely overlooked. Many of the pipes are barren of metallic minerals but carry sheared and healed quartz specimens. The principal Mo mine in the area, Maurer's Claim, is characterized by unusual, flattened, and doubly-terminated, smoky quartz crystals. These, together with molybdenite crystals, were commented on by some of the earliest writers on Kingsgate and the deposits were investigated for quartz during World War II. Some quartz crystals recovered during the last 15 years contain spectacular inclusions of bismuthinite

The structure of gillardite, the Ni-analogue of herbertsmithite, from Widgiemooltha, Western Australia

The structure of gillardite, the Ni-analogue [ideally Cu3NiCl2(OH)6] of herbertsmithite [ideally Cu3ZnCl2(OH)6] has been determined at 273(2) K. The crystal used was removed from a sample from the 132N nickel deposit at Widgiemooltha, Western Australia, Australia. Seventeen electron-microprobe analyses gave compositions, based on a total of four cations per formula unit, that ranged from (Cu3.189Ni0.803Co0.002Fe0.006)Cl2(OH)6 to (Cu2.922Ni1.058Co0.020)Cl2(OH)6, with an average result of all analyses of (Cu3.081Ni0.903Co0.012Fe0.004)Cl2(OH)6. The structure was refined using site occupancies indicated by the average composition, although refinement using the ideal composition gave identical results within standard errors. The new species gillardite is trigonal (rhombohedral), space group Rm, with a 6.8364(1), c 13.8459(4) Ã, Z = 3. The oxysalt is isostructural with herbertsmithite, with the two different sites in the paratacamite-type structure being occupied by different cations [paratacamite is Cu4Cl2(OH)6, space group R with a pronounced Rm substructure]. In gillardite, the Cu site is strongly Jahn–Teller-distorted, and the Ni site is regular with respect to Ni–O bond lengths, but with a slight angular distortion from regular octahedral geometry

Gillardite, Cu3NiCl2(OH)6, a new mineral from the 132 North deposit, Widgiemooltha, Western Australia

Gillardite, Cu3NiCl2(OH)6 (IMA 2006-041), is a new mineral from the 132 North deposit, Widgiemooltha, Western Australia, Australia. The name is in honour of Professor D. Gillard, in recognition of his contributions to the field of inorganic chemistry. It occurs as aggregates of equant crystals up to 0.5mm in size in a siicified ferruginous gossan, associated with a variety of secondary Ni and Cu minerals. Gillardite is rhombohedral, space group R3¯m, with single-crystal unit-cell parameters a=6.8364(1), c=13.8459(4)Ã3,Z=3,Dcalc=3.76g cm³. The ten strongest lines in the X-ray powder diffraction pattern [d in Ã(I)(hkl)] are 5.459(100)(101), 2.753(69)(113), 2.256(39)(204), 2.901(19)(201), 4.648(16)9003), 2.725(14)(202), 1.818(13)(303), 4.515(11)(102), 1.711(10)(220) and 3.424(8)(110). An average of 12 microprobe analyses (wt%) gave CuO, 55.6; 15.3; CoO, 0.2; FeO, 0.1; Cl, 17.3. One analysis (TGA) gave H2O, 13.1, less O=Cl, -3.9; total, 97.7. The derived empirical formula (based on 2 Cl pfu) is (Cu2.865Ni0.840Co0.006)Σ3.722Cl2(OH)5.960. Normalisation of the metal distribution to 4 metal ions pfu gives (Cu3.08Ni0.90Co0.01Fe0.01)Σ4.00Cl2(OH)5.96. Spot analyses show variation of Cu:Ni ratios and metal occupancies from (Cu3.135Ni0.853Co0.012) to (Cu2.922Ni1.058Co0.020). The simplified formula is thus Cu3.1Ni0.9Cl2(OH)6 or Cu3NiCl2(OH)6. The formula is entirely consistent with the results of a single-crystal X-ray structure analysis. Equant rhombohedral crystals showing the forms {101}, {021}, {0001} and {100} (probable) are dark green in colour and larger crystals are nearly black. No twinning was observed. Gillardite is non-fluorescent, has a green streak and is transparent with a vitreous lustre. Mohs hardness is 3, fracture is splintery and uneven, and cleavage is good on{101}. Gillardite is uniaxial (+), with ω=1.836 (0.002, ε=1.838 (0.002) (white light). No dispersion or pleochroism was observed. Gillardite is isomorphous with herbertsmithite, Cu3ZnCl2(OH)6, but can be conveniently distinguished from the latter by chemical analysis and a careful examination of X-ray powder diffraction data

Primary bismuth minerals from the Wolfram pipe, Kingsgate, New South Wales

Recent trial mining on the site of the Wolfram pipe on the Kingsgate field near Glen Innes, New South Wales, has unearthed a rich suite of bismuth minerals that have not been available for study since the early days of mining in the region. Aside from native bismuth and bismuthinite, Bi-rich mineralization carries significant amounts of galenobismutite and cosalite. Kobellite is locally abundant and represents a new primary mineral for Kingsgate. Other phases have been detected in small amounts, including treasureite. It is likely that the Bi-mineral suite at Kingsgate is more complex than has hitherto been thought