The blind Prominent Hill hematitic IOCG deposit occurs in a steeply-dipping overturned rock sequence with no surface exposures. Ore is localized within an interpreted Paleoproterozoic marine carbonate and siliciclastic unit whereas younger subaerial mafic-intermediate volcanic rocks and red beds physically underly the deposit. Geochemical data and previously-presented detrital zircon ages suggest that the younger rocks are equivalent to the ca 1.59 Ga Gawler Range Volcanics (GRV) in other parts of the Gawler Craton. However, in common with examples from near Olympic Dam, some of the volcanic rocks near Prominent Hill are strongly enriched in incompatible elements compared to GRV from type sections with no known IOCG association. Volcanic rocks at Prominent Hill are extensively altered and clearly predate the ore-forming hydrothermal system. In the more distal footwall they range from essentially unaltered to pervasively albitized. Albite was sequentially overprinted by chlorite, sericite (Mg-Fe illite) hematite and sulphides + carbonates and the development of the latter minerals increases towards the interpreted ca 1.6 Ga unconformity/disconformity and the orebody. These observations indicate that fluid flow associated with ore formation at Prominent Hill was focussed close to a major regional stratigraphic discontinuity at the base of the GRV-equivalent sequence.

Synchrotron radiation X-ray fluorescence (SR-XRF) was used to characterize As speciation within natural fluid inclusions from three deposits with different hydrogeochemical and geological settings. The studied samples represent different compositions of Au-bearing fluids: typical orogenic Au deposit (low-salinity, similar to 6 mol% CO(2) +/- CH(4); Brusson, Western Italian Alps); brines from a Proterozoic (Fe)-Cu-Au deposit (Starra, Queensland, Australia); and an As-rich magmatic fluid with a bulk composition similar to that typical of orogenic gold (Muiane pegmatite, Mozambique). Arsenic K-edge X-ray absorption spectra (XAS) were obtained from fluid inclusions at temperatures ranging from 25 to 200 C, and compared with spectra of aqueous As(III) and As(V) solutions and minerals. X-ray absorption near edge structure (XANES) data show that initially the fluid inclusions from all three regions contain some As in reduced form [As(III) at Brusson and Muiane; As-sulfide or possibly As(0) at Starra]. However, this reduced As is readily oxidized under the beam to As(V). Therefore, extended X-ray absorption fine structure (EXAFS) spectra for the As(III) aqueous complex could be collected only on the sample from the Muiane pegmatite containing large fluid inclusions with high As concentrations (>> 1000 ppm). Analysis of these EXAFS data shows that As(OH)3((aq)) (coordination number of 3.0 +/- 0.2 atoms, bond length of 1.76 +/- 0.01 angstrom) is the dominant arsenic aqueous species in the Muiane fluid inclusions at 100 degrees C, in accordance with predictions based on studies conducted using autoclaves. The As(V) complex resulting from photooxidation in the Muiane inclusions was characterized at 200 degrees C; the As-O bond distance (1.711 +/- 0.025 A) corresponds to that found in the arsenate group in minerals, and to that measured for the (HAsO(4))(2-) complex at room temperature (1.700 +/- 0.023 angstrom).The extent of the XAS information that could be obtained for As in this study was limited by the rapid photooxidation that occurred in all inclusions, despite the relatively low photon flux density used (similar to 4.4 x 10(6) photons/s/mu m(2)). Photosensitivity was not observed in autoclave experiments and is the result of a complex interaction between redox-sensitive complexes in solution and the products of water radiolysis generated by the beam. Even under such challenging experimental conditions, the information gathered provides some precious information about As chemistry in ore-forming fluids.

We are happy to report that the total number of initial manuscript submissions in 2009 will be more than 120, the highest ever recorded for Mineralium Deposita in a single year. This is positive news for the journal, particularly in the light of its most recent impact factor of 2.04 also being the highest it has ever achieved. In part, the increasing submissions reflect the growing engagement of the developing world and the erosion of historical barriers, including linguistic ones, that previously inhibited many scientists from presenting their work to international journals. These trends are good not only for the journal and for science and the global community in general but also bring some challenges, not the least of which is an increasing workload for the Editorial Board. We have therefore been working to both increase the number and diversify the international representation of the Board membership.

Reports of chloride substitution in common natural sulphides are lacking but are predictably influenced by key variables in hydrothermal systems including T, pH, Eh aCl(-), and aHS(-). Materials scientists have long recognized that "II-VI compounds" (e.g. sphalerite) may accommodate halogens with charge balance maintained by cation deficiencies (e.g. Zn1-0.5xS1-xClx). The majority of around 200 analyses of sphalerite from the Century Zinc mine (NW Queensland) reveal chlorine above electron microprobe detection limits with a maximum of ca 2200 ppm. The analyses support the Zn deficiency substitution although a small subset reveal a 1:1 (molar) correlation of Cl with the highest (Cu+Ag) implying an additional coupled substitution mechanism. Colloform sphalerite from the Galmoy mine (Ireland) has variable concentrations of Cl up to 6000 ppm in growth zones also displaying variations of Fe and Cd. The chlorine content of sphalerite may therefore provide a new tool to characterize the evolution of conditions in hydrothermal ore deposits.

Proterozoic rocks of the Cloncurry district in NW Queensland, Australia, are host to giant (tens to hundreds of square kilometers) hydrothermal systems that include (1) barren regional sodic–calcic alteration, (2) granite-hosted hydrothermal complexes with magmatic–hydrothermal transition features, and (3) iron oxide–copper–gold (IOCG) deposits. Fluid inclusion microthermometry and proton-induced X-ray emission (PIXE) show that IOCG deposits and the granite-hosted hydrothermal complexes contain abundant high temperature, ultrasaline, complex multisolid (type 1) inclusions that are less common in the regional sodic–calcic alteration. The latter is characterized by lower salinity three-phase halite-bearing (type 2) and two-phase (type 3) aqueous inclusions. Copper contents of the type 1 inclusions (>300 ppm) is higher than in type 2 and 3 inclusions (<300 ppm), and the highest copper concentrations (>1,000 ppm) are found both in the granite-hosted systems and in inclusions with Br/Cl ratios that are consistent with a magmatic source. The Br/Cl ratios of the inclusions with lower Cu contents are consistent with an evaporite-related origin. Wide ranges in salinity and homogenization temperatures for fluid inclusions in IOCG deposits and evidence for multiple fluid sources, as suggested by halogen ratios, indicate fluid mixing as an important process in IOCG genesis. The data support both leaching of Cu by voluminous nonmagmatic fluids from crustal rocks, as well as the direct exsolution of Cu-rich fluids from magmas. However, larger IOCG deposits may form from magmatic-derived fluids based on their higher Cu content.

[Extract] Geochemical zonation in the breccia-hosted Ernest Henry iron-oxide-Cu-Au deposit of the Proterozoic Mt Isa Block occurs in an oscillatory fashion at micro-scales and irregular to broadly concentric fashions at broader scales.

The Ernest Henry Cu–Au deposit was formed within a zoned, post-peak metamorphic hydrothermal system that overprinted metamorphosed dacite, andesite and diorite (ca 1740–1660 Ma). The Ernest Henry hydrothermal system was formed by two cycles of sodic and potassic alteration where biotite–magnetite alteration produced in the first cycle formed ca 1514±24 Ma, whereas paragenetically later Na–Ca veining formed ca 1529 +11/−8 Ma. These new U–Pbtitanite age dates support textural evidence for incursion of hydrothermal fluids after the metamorphic peak, and overlap with earlier estimates for the timing of Cu–Au mineralization (ca 1540–1500 Ma). A distal to proximal potassic alteration zone correlates with a large (up to 1.5 km) K–Fe–Mn–Ba enriched alteration zone that overprints earlier sodic alteration. Mass balance analysis indicates that K–Fe–Mn–Ba alteration—largely produced during pre-ore biotite- and magnetite-rich alteration—is associated with K–Rb–Cl–Ba–Fe–Mn and As enrichment and Na, Ca and Sr depletion. The aforementioned chemical exchange almost precisely counterbalances the mass changes associated with regional Na–Ca alteration. This initial transition from sodic to potassic alteration may have been formed during the evolution of a single fluid that evolved via alkali exchange during progressive fluid-rock interaction. Cu–Au ore, dominated by co-precipitated magnetite, minor specular hematite, and chalcopyrite as breccia matrix, forms a pipe-like body at the core of a proximal alteration zone dominated by K-feldspar alteration. Both the core and K-feldspar alteration overprint Na–Ca alteration and biotite–magnetite (K–Fe) alteration. Ore was associated with the concentration of a diverse range of elements (e.g. Cu, Au, Fe, Mo, U, Sb, W, Sn, Bi, Ag, F, REE, K, S, As, Co, Ba and Ca). Mineralization also involved the deposition of significant barite, K(–Ba)–feldspar, calcite, fluorite and complexly zoned pyrite. The complexly zoned pyrite and variable K–(Ba)–feldspar versus barite associations are interpreted to indicate fluctuating sulphur and/or barium supply. Together with the alteration zonation geochemistry and overprinting criteria, these data are interpreted to indicate that Cu–Au mineralization occurred as a result of fluid mixing during dilation and brecciation, in the location of the most intense initial potassic alteration. A link between early alteration (Na–Ca and K–Fe) and the later K-feldspathization and the Cu–Au ore is possible. However, the ore-related enrichments in particular elements (especially Ba, Mn, As, Mo, Ag, U, Sb and Bi) are so extreme compared with earlier alteration that another fluid, possibly magmatic in origin, contributed the diverse element suite geochemically independently of the earlier stages. Structural focussing of successive stages produced the distinctive alteration zoning, providing a basis both for exploration for similar deposits, and for an understanding of ore genesis.

Ernest Henry is an iron oxide-copper-gold deposit characterized by magnetite≫hematite, chalcopyrite as the only significant hypogene copper mineral. It occurs within a large, zoned, medium to high temperature alteration system. Pre- to synmineralization quartz contains three broad populations of fluid inclusions. Type 1 (L-V-H±nS) inclusions decrepitate or homogenise at 200–500° C, have salinities of 32–55 wt% NaClequiv, display chemical variations that parallel the paragenetic sequence of alteration, and have variable Br/Cl mostly less than magmatic brines. Type 2 (L-V) inclusions homogenise at temperatures of 120–350°C have salinities up to 20 wt% NaClequiv and inferred to contain CaCl2. Type 3 L-rich CO2 inclusions were entrapped at 130–370MPa. dD and dO of pre- to synmineralisation fluids are estimated to have been −23 to −66 and 8 to 11 per mil respectively. dS in main ore pyrite and chalcopyrite is −1.6 to +5.4 per mil. The data are compatible with a substantial magmatic contribution to Ernest Henry fluids but also suggest the system was complex and involved fluids and other components with different sources. Ernest Henry is distinguished from the giant Olympic Dam deposit by evidence for high temperature/salinity fluids and for no major involvement of surficial waters during mineralization.

Digital SEM imagery including X-ray mapping and spectral cathodoluminescence (CL) studies support the previously-proposed diagenetic replacement mode of origin for the large Proterozoic shale/siltstone-hosted Century zinc deposit in northwest Queensland. CL effectively distinguishes different generations of quartz and sphalerite and reveals that the weakly mineralized silt-stone beds were replaced by locally pervasive diagenetic silica and microconcretionary siderite prior to ore deposition. This may have destroyed the depositional permeability of these rocks and promoted infiltration of mineralizing fluids into the shale bands in the ore sequence. Micro-replacement textures in which sphalerite has replaced pyrobitumen, pyrite and siderite are incompatible with thermochemical sulphate reduction model for mineralisation and favour a mechanism involving a chemically-reduced, sulphur-bearing ore fluid with metal transport, possibly facilitated by organic complexes. Zn in microconcretionary siderite records the infiltration of sulphur-poor, zinc-bearing fluids prior to main phase sphalerite mineralization. Late stage honey coloured sphalerite has similar Mn and Fe contents but weak CL compared to main phase sphalerite. The time interval represented by the two mineralization phases is unknown.

From the first issue in 1905 onward, Economic Geology has been the main publication for those who study mineral deposits; indeed, it is now difficult to imagine economic geology without Economic Geology. It is interesting to ask, therefore, Who were the farsighted people who founded the journal, and Why did they think a specialized publication devoted to mineral deposits was needed?Let us first address the question, Who were the founders? They were the 12 men who collectivelydecided a new publication was needed, who then planned the financial structure to support the venture, and who served as the original editorial group. All were employed by, or associated with, the U.S. Geological Survey. Josiah Edward Spurr suggested the need for a journal sometime in November or December 1904. After informal discussions, nine of the founders met in the office of Waldemar Lindgren in the headquarters of the U.S. Geological Survey in Washington, D.C., on May 16, 1905, and founded the Economic Geology Publishing Company. The sole purpose of the company was the publication of a journal ‘...devoted primarily to the broad application of geologicprinciples to mineral deposits of economic value, and to the scientific description of such deposits, and particularly to the chemical, physical, and structural problems bearing on their genesis.’ Initial financing for the new company was raised by the sale of 80 shares at a cost of $25 per share.Eight of the men at the founding meeting formed the first board of directors; Spurr was president, Frederick L. Ransome, secretary, and George O. Smith, treasurer. Other members were Arthur H. Brooks, Marius R. Campbell, Walter H. Weed, Waldemar Lindgren, and a young academic from Lehigh University in Pennsylvania, John D. Irving. Theninth man at the meeting was H. Foster Bain. Irving was appointed editor. Lindgren, Ransome, and Campbell from the U.S. Geological Survey, together with three academics, James F. Kemp of Columbia University, Heinrich Ries ofCornell University, and Charles K. Leith of the University of Wisconsin, were appointed associate editors. The initial board members, the editor, and associate editors are the people we now recognize as the founders of Economic Geology. Two others, Frank D. Adams, of McGill University in Canada, and John. W. Gregory, of Glasgow University in Scotland, were subsequently added as associate editors, and a third person, W. S. Bayley of the University of Illinois, was appointed as business editor, but

El Galeno and Michiquillay are early to middle Miocene Cu–Au–Mo porphyry-related deposits located in the auriferous Cajamarca district of northern Peru. The El Galeno deposit (486 Mt at 0.57% Cu, 0.14 g/t Au and 150 ppm Mo) is associated with multiple dioritic intrusions hosted within Lower Cretaceous quartzites and shales. Emplacement of the porphyry stocks (17.5–16.5 Ma) in a hanging wall anticline was structurally controlled by oblique faults superimposed on early WNW-trending fold-thrust structures. Early K-feldspar–biotite–magnetite (potassic) alteration was associated with pyrite and chalcopyrite mineralisation. A quartz–magnetite assemblage that occurs at depth has completely replaced potassically altered rocks. Late- and post-mineralisation stocks are spatially and temporally related to weak quartz–muscovite (phyllic) alteration. High Au grades are associated with early intrusive phases located near the centre of the deposit. Highest Cu grades (~0.9% Cu) are mostly associated with a supergene enrichment blanket, whilst high Mo grades are restricted to contacts with the metasedimentary rocks. The Michiquillay Cu–Au–Mo deposit (631 Mt at 0.69% Cu, 0.15 g/t Au, 100–200 ppm Mo) is associated with a Miocene (20.0–19.8 Ma) dioritic complex that was emplaced within the hanging wall of a back thrust fault. The intrusive complex is hosted in quartzites and limestones. The NE-trending deposit is crosscut by NNW-trending prospect-scale faults that influenced both alteration and metal distribution. In the SW and NE of the deposit, potassic alteration zones contain moderate hypogene grades (0.14 g/t Au and 0.8% Cu) and are characterised by chalcopyrite and pyrite mineralisation. The core of the deposit is defined by a lower grade (0.08 g/t Au and 0.57% Cu) phyllic alteration that overprinted early potassic alteration. Michiquillay contains a supergene enrichment blanket of 45–80 m thickness with an average Cu grade of 1.15%, which is overlain by a deep leached cap (up to 150 m). Cu–Au–Mo (El Galeno-Michiquillay) and Au-rich (Minas Conga) deposits in the Cajamarca region are of similar age (early–middle Miocene) and intrusive rock type (dioritic) associations. Despite these geochronological and geochemical similarities, findings from this study suggest variation in metal grade between the hybrid-type and Au-rich deposits result from a combination of physio-chemical factors. These include variations in temperature and oxygen fugacity conditions during hypogene mineralisation resulting in varied sulphide assemblages, host rock type, precipitation of ubiquitous hydrothermal magnetite, and late hydrothermal fluid flow resulting in a well-developed phyllic alteration zone.

High salinity fluid inclusions (Th=200–550°C) from the Broken Hill and Cannington “Broken Hill-type” ore deposits in Australia have been analysed by PIXE and LA-ICP-MS. They have high Pb (>1%) and Zn (>1000 ppm) and Pb/Zn ratios much higher than those of the majority of crustal brines. Laser Raman studies reveal the presence of methane and PIXE images show that Pb and Zn are respectively concentrated in a Pb-K-Cl solid, and the liquid phase. This indicates that the inclusions have very low total sulphur contents. The Pb/Zn ratios are similar to those of eutectic melts in the Gn-Sp-Po system whereas Pb/Fe ratios are variable and lower than those of such melts. If these brines originated by fractionation from synmetamorphic sulphide-rich melts, then they must been greatly modified prior to entrapment. An alternative origin involving late-to post-metamorphic interaction of externally-derived brines with pre-existing sulphide accumulations should also be considered. In either case, the unique brine chemistry would appear to relate to the large amounts of sulphides in these systems.

The Mount Isa Block (MIB) preserves evidence of significant hydrothermal alteration produced during multiple periods of veining, brecciation and alteration during the Paleo- and Mesoproterozoic. Representing the last phase, are large, quartz-rich veins that form long N-S vein systems associated with brittle movement along major N-S Paleoproterozoic faults. The Cloncurry Fault represents one such system where late quartz veins formed during dilation associated with left-lateral movement. Stable isotope data for these veins show that the fluids had a calculated (at 250degreesC) delta(18)O and deltaD of -4 to +3 parts per thousand, and - 22 to -4 parts per thousand, respectively, which suggests they were of mixed low-latitude meteoric fluid and formation water origin, and are markedly different to the fluids associated with earlier epigenetic Cu-Au mineralization and Na-Ca alteration. The low-latitude character of the hydrothermal system suggests it was formed near to the equator, and correlation to the paleomagnetic data for the MIB, together with structural and geological considerations, and geochronological arguments suggest they formed c. 1.10 Ga or later, some 400 m.y. after Na-Ca alteration and mineralization. These results suggest that the late veining was unrelated to earlier hydrothermal alteration, and as such places into doubt previous models of the evolution of mineralisation and alteration in the Eastern Fold Belt (EFB).

Amphibolites typically lacking visual signs of Pb–Zn mineralization are associated with pelitic gneisses at the Cannington and Maramungee ‘Broken Hill-type’ Pb–Zn–Ag deposits in the eastern Mount Isa Inlier. Within 150 m of the sulphide-rich lodes these have consistently anomalously high chalcophile metal contents. The enrichments broadly mimic the primary distinctions between the two deposits in respect to the relative abundances of Zn, As and Pb. At Maramungee, metal concentrations of thin amphibolites broadly increase towards the mineralized rock body and comparison with data from gneisses illustrates the general superiority of basic rocks as a sample medium due to their inherently low Pb-content and comparatively homogenous primary chemistry. Most amphibolite at Cannington occurs in a single metamorphosed sill that is consistently anomalous, though with irregular chalcophile element distributions. Petrographic and SEM studies show that the metal enrichments are related to sulphides in complex retrograde parageneses which have selectively replaced metamorphic (calcic) plagioclase. Most galena occurs as sub-10 μm grains. Chalcophile elements were dispersed in a hydrous fluid and selectively enriched in the amphibolites during retrograde metamorphism under greenschist to sub-greenschist facies conditions. Routine analysis of basic rocks for Pb (and Zn) might therefore provide a simple proximity indicator for Broken Hill-type deposits, especially in poorly exposed terrains where amphibolites are the most common cause of magnetic anomalies tested by exploration drilling.

Diopside-rich, skarn-hosted, copper–gold ore derived primarily from carbonaceous metapelites at Mount Elliott forms a distinctive member of the spectrum of Cu–Au–(Fe oxide) deposit styles in the Cloncurry district of the Paleoproterozoic to Mesoproterozoic Mount Isa Block. The mine sequence is a package of carbonaceous metapelites and metagreywackes containing amphibolites derived from tholeiitic basic rocks. A 40Ar–39Ar age spectrum with an extensive plateau-like segment at 1,510 ± 3 Ma from an actinolite associated with sulfides is taken to represent the age of mineralization and is identical within error to the ages of most of the nearby batholithic granitoids. The mine sequence is locally intruded by 1- to 10-m-thick late- to post-tectonic trachyandesite dykes, which were emplaced during the hydrothermal activity that created the orebodies and have affinities with the regional high potassium “Eureka” supersuite granitoids. Stable isotope data are consistent with dominantly magmatic fluids during mineralization and the regionally distinctive skarn (Ca–Mg) and Cu–Au–Ni–Co–Te–Se (low Pb–Zn–Ag–Sb) chalcophile element associations may reflect a primitive magmatic fluid source and/or leaching of these elements from country rocks. Mount Elliott is an unusual skarn deposit characterized by pronounced early albitization (K–Fe–Mg depletion) of the host rocks succeeded by predominantly open-space deposition of sodic diopside ± actinolite ± scapolite ± andradite ± magnetite ± sulfides ± apatite ± allanite ± tourmaline ± calcite. The Ca–Fe–Mg(–Na)-rich (manganese-poor) chemistry was imposed from the fluid phase in the absence of carbonate-rich protoliths. Immobile trace element (Ti, Zr, Nb) geochemistry shows that Mount Elliott skarns formed in both metasedimentary and mafic metavolcanic host rocks, but the former are the main hosts of ore in upper and lower ore zones that represent most of the resource. Banded skarns derived from a distinct calc-silicate/marble package at the nearby SWAN prospect have higher Nb/TiO2 and Zr/TiO2 ratios than the Mount Elliott metasediment-derived skarns, consistent with different provenance of the detrital components in the two sequences. Medium- to coarse-grained massive skarn and skarn breccia in the Mount Elliott lower ore zone formed in pelites and the trachyandesite dykes are the only intrusive rocks that could be genetically related to the mineralization in the immediate vicinity of the orebodies.