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By D Kepert

It is the role of the exploration geologist to create wealth through the discovery, delineation and characterisation of economic mineralisation. This requires a critical depth of geological understanding.Unfortunately, the resource industry is well known for its cyclic nature. Many of the current generation of workers have only ever experienced the boom of the ‘super-cycle’ and are only just discovering the negative side to the business. For the case of the geologist and especially the exploration geologist, the magnitude of peaks and troughs are usually amplified and may become destructive to all parties. During the uptime a healthy stream of exploration good news becomes the staple diet of company releases, in particular those of junior companies attempting to bolster the share price. The geological knowledge and experience gained thus forms a significant and integral part of the value and therefore, future of a company. On the downturn it is often viewed that geologists are a luxury, an optional extra and a burden on the bottom line with companies entering a period of memory loss and myopia.Retention of geological knowledge however remains critical as projects, companies and cycles mature. Beyond exploration per se, this knowledge becomes both fundamental in de-risking and commercialising an asset (through development or divestment) and in positioning the company for cyclic or counter-cyclic opportunities.The growth and retention of this knowledge base is difficult to quantify in terms of direct value but becomes one of a successful resource companies greatest assets. At worst, its loss can lead to millions of investors’ funds wasted on missed opportunities, drilling, or poorly designed plant and mine.But the rocks are around for the longer haul and pay little notice to the vagaries of the scurrying of Man.This paper reflects on some of the authors own observations through 25 years of iron ore exploration, in why it is critical to always rigorously question the prevailing geological (mis)understanding and the technical and commercial benefits which that may bring, and looks forward to the future.CITATION:Kepert, D, 2015. Geology – the affirmative case, in Proceedings Iron Ore 2015, pp 285–298 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 13, 2015

By M. J. McLeod, D. R. Lux, R. P. Taylor

"The Mount Douglas Granite constitutes the eastern part of the Saint George Batholith and contains the youngest, most differentiated phases of the batholith. It also contains extensive endogranitic, low-grade. Sn- W-Mo-bearing sheeted vein systems. Early phases of the Mount Douglas Granite are coarse- to medium-grained, seriate granites that represent the slowly cooled carapace of the intrusion. Late phases are medium- to fine-grained, equigranular and porphyritic granites that were accompanied by repeated and widespread fracturing of the carapace and injection of mineralizing fluids. These granites represent a highly differentiated suite with ""A "" type affinities developed in a ""within plate"" transitional to ""syn-collision"" tectonic setting. 4oAr/ 39Ar dates for biotites from the various phases indicate emplacement circa 367 Ma.The linear distribution of some phases in the Mount Douglas Granite and the systematic orientations of sheeted veins along tensional fractures indicate structural control on granite emplacement and vein distribution. This type of relatively passive endogranitic mineralization is unique in the granites of southern New Brunswick and contrasts markedly with highly fluidized systems operative elsewhere in the area. IntroductionInvestigation of Sn-W-Mo occurrences in New Brunswick has shown that most of this mineralization is associated with late, highly differentiated phases of post-orogenic (Acadian) granitoid magmatism that occurred during Devonian and Early Carboniferous time (Ruitenberg and Fyffe, 1982; Taylor et al., 1988). The polymetallic Mount Pleasant Sn-W-Mo deposit (Ruitenberg, 1967, 1972; Kooiman et al., 1986)and the Burnt Hill W deposit are two orebodies of this type in New Brunswick. Numerous smaller deposits associated with these granitoid rocks in southwestern New Brunswick have been documented in previous investigations (Ruitenberg, 1967, 1968; Ruitenberg and Fyffe, 1982; Taylor et al., 1985; Lentz, 1985)."

Jan 1, 1988

By A Madera, R Watt

The Tampakan deposit is a strongly telescoped high-sulphidation-epithermal/ porphyry deposit pair which is hosted by a sequence of probable Pliocene age subaerial andesite flows. These host units lie on the western flank of a deeply dissected andesitic stratovolcano within the northernmost portion of the Sangihe Arc in southern Mindanao. The deposit was discovered by WMC geologists in 1992 and is currently undergoing resource evaluation. Preliminary resource estimations indicate a total inferred metal content of 12 million tonnes of copper metal and 16 million ounces of gold. Using a 0.2 per cent Cu cut-off grade, the deposit has a current mineral resource of approximately 2.5 billion tonnes with an estimated grade of 0.48 per cent copper. At a higher cut-off grade of 0.5 per cent Cu, the mineral resource is approximately 900 million tonnes with an estimated grade of 0.75 per cent copper. Mineralisation is open both to the west and at depth. The Tampakan district is centrally located with respect to a 100 km wide zone of left-lateral strike-slip deformation represented by the trans-Mindanao Cotabato Fault Zone. The district is transected by several WNW-striking wrench faults which represent strands of the regional Cotabato Fault Zone. High-sulphidation epithermal mineralisation within the Tampakan deposit is strongly controlled by NNE-trending faults which lie along a dilational orientation within the Pliocene stress field associated with the Cotabato strike-slip fault zone. The mineralisation is broadly hosted by a gently-dipping, tabular zone of partial to massive silicification which displays multi-phase brecciation, acid-leaching, related vuggy porosity and which is developed within a district-scale advanced-argillic and argillic lithocap exceeding 90 km 2 in area. High-sulphidation epithermal mineralisation is associated with a silica-pyrophyllite-dickite-alunite-diaspore¦sericite alteration assemblage which is transitional downward to sericite-chlorite alteration and relict potassic biotite-chlorite-magnetite-anhydrite alteration associated with pervasively developed but weakly mineralised porphyry quartz stockwork veins. The high-sulphidation mineralisation is dominated by disseminated, vein and vug-filling enargite-bornite-digenite-chalcocite-covellite ¦ molybdenite which has overprinted an earlier phase of porphyry copper stockwork veins associated with high-level porphyritic hornblende diorite stocks. The distribution of high-sulphidation alteration and mineralisation reflects strong stratigraphic and structural controls. The high-sulphidation mineralisation covers a surface area of approximately 1.6 km by 2.0 km and forms a tabular, flat-lying to gently-dipping body between 200 and 500 metres thick. It is intersected at RL-1200 m ASL (at surface) in the northern portion of the deposit and extends down to RL-600 m ASL at the southern end. The deposit has been diamond-drill tested to a depth of 400 - 500 metres where low-grade chalcopyrite-bornite-pyrite mineralisation is hosted by pervasive quartz stockwork veins. This deep-level mineralisation represents the outer portion of a porphyry Cu system hosted by both andesite flows and the uppermost portions of high-level hornblende diorite stocks. Deep drilling to test for higher tenor porphyry Cu mineralisation is planned.

Jan 1, 1999

By C. DeLong

"The Mt. Milligan porphyry copper-gold deposits are in central British Columbia, 155 km northwest of Prince George. Mineralized outcrops and float were discovered in the Mount Milligan area by prospecting. The most recent discoveries, which utilized lithogeochemistry, were in 1983. Areas containing the outcrops and float then were investigated by geological mapping, soil and lithogeochemical sampling, ground and airborne geophysical surveys, trenching and diamond drilling. This work led to the discovery of the Mt. Milligan Main deposit in 1987 and the Southern Star deposit in 1989. Extensive diamond drilling continued until 1991 and delineated a measured and indicated resource of 299 million tonnes grading 0.45 g/t Au and 0.22 % Cu from the combined deposits.The Mt. Milligan deposits lie within the Early Mesozoic Quesnel Terrane and are hosted by porphyritic monzonite stocks and adjacent volcanic rocks of the Takla Group. The Mt. Milligan Main deposit is centred around the MBX stock and Rainbow dike, and the Southern Star deposit around the Southern Star stock.Potassic alteration is extensive within the stocks and in volcanic rocks adjacent to the MBX stock and Rainbow dike. Propylitic alteration surrounds the potassic alteration and decreases in intensuy away from the stocks. Mineralization consists mostly of pyrite, chalcopyrite, lesser magnetite, and minor bornite, molybdenite and gold.Mineralogical zoning is well-developed within the deposits. A biotite-rich subzone forms the core of the potassic alteration zone and hosts most of the copper and gold. Numerous polymetallic veins lie within the propylitic alteration zone just beyond the limit of porphyry-style copper-gold mineralization."

Jan 1, 1995

By D. K. Jorgensen

The Bullfrog and Montgomery-Shoshone deposits, near Beatty, NV, have a combined drill-indicated reserve of 15.8 Mt (17.4 million st) of ore. Average grade is 3.5 g/t (0.103 oz per st) gold and 8.2 g/t (0.24 oz per st) silver. The deposits occur in Miocene volcanic rocks that underwent large-scale movement within a detachment-faulted terrane. The principal host to gold mineralization is a strongly welded rhyolitic tuff that experienced brittle deformation during plate movement. Open space fractures and breccia were filled with quartz, calcite, and adularia accompanied by lesser pyrite, gold, and acanthite. Gold occurs as micrometer-sized particles within and adjacent to the low-angle fault and along associated listric-normal and tear faults. The Bullfrog and Montgomery-Shoshone are volcanic-hosted, detachment fault-related, epithermal quartz calcite stockwork gold deposits. Bullfrog's minable reserve is 13 Mt (14.3 million st) of ore grading 3.8 g/t (0.11 oz per st) of gold. At Montgomery-Shoshone, 2.7 Mt (3 million st) minable tons at 2.5 g/t (0.072 oz per st) are present. Preproduction stripping has begun at the Bullfrog ore body. A 7.7-kt/d (8500-stpd) carbon-in-pulp (CIP) mill is under construction. In 1990, Bond Gold expects to be producing about 6.2 t/a (200,000 oz per year) of gold.

Jan 1, 1990

By J. Beland

The Rimouski-Matapedia region is along the southwestern extension of the central Siluro-Devonian synclinorium of Gaspe Peninsula. As in Gaspe about 30,000 feet of Siluro-Devonian strata rest on a "basement" of tightly folded Ordovician rocks. The central synclinorium is divided up into two northeasterly trending belts each of which is characterized by distinctive lithologies and patterns of folding. The northwestern belt is gently to moderately folded and includes lithologies which point to a stable environment. The southeastern belt on the other hand is tightly folded and the lithologies indicate a less stable environment. A marked angular unconformity separates the basement from the Siluro-Devonian cover near the north-western margin of the northwestern belt. At the southeastern margin of the southeastern belt the relationship of cover to basement has not been as-certained because of a fault. The northwestern belt has several features significant in the search for petroleum; the Silurian strata are exposed in broad open anticlines

Jan 1, 1962

By Edward D. Elkins

CalMat Co. is one of the largest producers of construction aggregates in the United States. The CalMat Reliance plant is located in Irwindale, California, and is situated on an alluvial fan formed by the San Gabriel River. The fan deposits are of Quaternary age and were derived from granitic and metamorphic bedrock exposed in the San Gabriel Mountains to the north. The sediments are poorly sorted and range in size from large boulders to clay size particles. The coarse material is hard and durable and consists of quartz diorite, granodiorite, granitic gneiss, schist and minor amounts of volcanic rock. The matrix is comprised of silty sand with varying amounts of clay. Thin silt and clay lenses occur sporadically throughout the deposit. The clay content of the matrix and the degree of weathering of the coarse material increases with depth. Based on seismic data, the alluvial fan varies from 200 to 400 feet thick and overlies crystalline bedrock. The Reliance plant was constructed in 1971 and 1972. It has a nominal capacity of 1200 to 1400 tons per hour, and typically produces more than three million tons of aggregate products per year. Alluvial fan sediments are mined from a gravel pit situated adjacent to the plant. The material is fed through a mobile, 48- by 60-inch, in-pit jaw crusher, then transported by conveyor to the main plant to be processed. The plant is modern and highly efficient. It has a typical wet and dry circuit and is capable of producing a wide range of aggregate products. To extend the life of the plant, a 9,000 foot conveyor system is being constructed to connect it to a granite quarry operated by Azusa Rock Inc. The quarry is located north of Irwindale, and is 50 percent owned by CalMat Co. The conveyor will be used to export crushed rock from the quarry to Reliance. The existing plant will be modified to process the crushed rock.

Jan 1, 1995

By Z S Chang, T F. Zhou, G X. Zhong

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. The Yaojialing zinc-gold polymetallic deposit is a newly discovered, large skarn deposit in the Middle-Lower Yangtze metallogenic belt, East China. It is located in the transitional zone between the Tongling uplift block and the Fanchang faulted basin. It is mainly hosted in the contact zone between early Cretaceous granodiorite porphyry and Carboniferous-Triassic limestone, or occurs in limestone xenoliths within the intrusion. Skarn and stratabound massive sulfide orebodies are the primary ore styles. Sulfide ?34SV-CDT values indicate a magmatic sulfur source, in common with most deposits in the Tongling block. Calcite d13CV-PDB and d18OV-SMOW ratios reveal that marine carbonates were the major source of carbon in late-stage hydrothermal fluids. The calcite probably formed during interaction between magmatic fluids and carbonate wall rock.CITATION:Zhong, G X, Zhou, T F and Chang, Z S, 2015. Geology, chronology and isotope geochemistry of the Yaojialing zinc-gold deposit, Tongling ore district, Anhui Province, China, in Proceedings PACRIM 2015 Congress, pp 457–462 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By Johan K. Rodenburg

A major bauxite belt was discovered and evaluated from 1969 to 1974 by P. T. Alcoa Minerals of Indonesia in West Kalimantan, Indonesia. The proven reserves of beneficiated bauxite are 800 million tons averaging 38.6% AA1203 and 3.0% RSiO2. Inferred reserves of washed bauxite are in excess of 2 billion tons. The bauxite occurs as capping of low lying hills which were formed during the post Paleogene peneplaination stage. The overburden varies from 0.6 to 3.8 meters and the nodular bauxite horizon from 2.2 to 5.2 meters. The deposits were formed by the in situ weathering of predominantly acidic and basic intrusive rocks.

Jan 1, 1984

By Howard Brown

High purity, high brightness limestone deposits in the San Bernardino Mountains and Mojave Desert region occur in upper Paleozoic carbonate rocks which are part of an upper Precambrian and Paleozoic sequence that unconformably overlies crystalline basement. The Paleozoic strata are divided into formations and members, and correlated with strata of the inner Cordilleran miogeocline. The region has been affected by multiple Mesozoic intrusive, contact, and regional metamorphic events. Structure is complex, and includes polyphase Mesozoic folding and thrusting, and complex Cenozoic structures. The area continues to be seismically active. High brightness (white), high purity crystalline limestone deposits are uncommon because their formation is dependent on several geologic processes which include; 1) depositional environment, 2) contact and or regional metamorphism, 3) folding and faulting, 4) uplift and erosion, and 5) preservation through geologic time. The complex geologic history of the San Bernardino Mountains and Mojave Desert region has allowed the formation of several large high brightness, high purity limestone deposits which are currently being mined or will be mined in the future. Specialty Minerals, Inc. (formerly Ptizer), Pluess-Staufer (California), Inc. and Partins Limestone, Inc. produce high brightness, high purity limestone from several quarries in the San Bernardino Mountains. These active mines combined with undeveloped deposits controlled by Pluess-Staufer in the San Bernardino Mountains, New York Mountains, and Bristol Mountains in the Mojave area, contain proven and or indicated reserves sufficient to sustain production through the 21st century Detailed geologic mapping, intimate knowledge of stratigraphy, recognition of complex structures, sampling, drilling and assay data, are proven tools in the discovery and delineation of high brightness, high purity limestone deposits in the San Bernardino Mountains and Mojave Desert region of southern California.

Jan 1, 1995

By H. J. Brown

Pluess-Staufer (California) Inc. Lucerne Valley California operation is one of the largest producers of high brightness high purity fme grind limestone products in western North America. The San Bernardino Mountains area of southern California contains the largest high brightness, high purity limestone mining operations and undeveloped reserves in western North America (Fig. 1, Brown 1987). Combined annual production of high brightness limestone products from several operations is approximately 1.5 million tons, with an estimated gross value of $75 million dollars per year (Fig. 2). An additional 5.0 million tons of cement grade limestone is mined by several large cement producers in the nearby Mojave area (Brown, in press). The purpose of this paper is to summarize the geologic setting, genesis and mining of white, high purity crystalline limestone by Pluess-Staufer (California) Inc.

Jan 1, 1994

By AMIRA P588 Research Team

This contribution summarises new knowledge and data, obtained during a three year ARCAMIRA funded research project, on the mineralogical and geochemical characteristics of hydrothermal alteration associated with low sulfidation, gold-silver epithermal deposits. These data are used to develop exploration vectors for use at both deposit and district scales, plus techniques have been established to distinguish ore grade epithermal systems from barren or low grade systems. Deposits investigated were Ladolam, Papua New Guinea, Gosowong and Mt Muro, Indonesia, Cerro Vaguardia, Argentina and Bimurra and Twin Hills, Australia.

Jan 1, 2005

By Xuanxue Mo, Zengqian Hou

"Abstract -Yidun Island Arc in Sanjiang Region is one of the important Kuroko-type volcano­ genic massive sulfide deposits (VMS) districts in southwestern China. Tectonically, the region is situated in the eastern portion of the Tethys orogenic belt, and is a late Triassic extensional island-arc. The island-arc underwent earlier arc construction, intra-arc rifting, later arc construction and back­ arc spreading during its evolution and formed a complete trench-arc-basin system, i.e., the Ganzi­ Litang suture zone, forearc basin, outer arc, intra-arc rifting zone, inner arc and back-arc basin from east to west across the island-arc.Kuroko-type VMS deposits and occurrences discovered so far are limited to within the intra-arc rifting zone of the Yidun Island Arc and tend to occur in groups or clusters distributed in separate fault­ bound basins; e.g., Zengke, Gacun and Xiangcheng basins, in which submarine volcanic rocks, especially bimodal volcanic suites, were extensively developed. The VMS deposits formed in the waning stages of volcanic eruption in the late Triassic and are hosted in the uppermost section of acidic volcanic rocks (rhyolitic-dacitic) within a bimodal suite. The orebodies are associated with these host rocks: rhyolitic-dacitic pyroclastic rocks and exhalites and chemical sedimentary rocks.Ali VMS deposits in Sanjiang are of the Zn-Pb-Cu type. The architecture of the deposits is two­fold, consisting of concordant lenses and layers of massive sulfides and an underlying discordant stockwork. Ali deposits show metal zoning. The hydrothermal alteration related to mineralization is strong and asyrnmetrical, and is found dominantly within the stockwork zone and host rocks surrounding the ores. There are two alteration patterns: (1) chloritization - sericitization - silicification from outer sides to core of the alteration pipe; and (2) silicification + sericitization - silicification + carbonate from the lower to upper part of the alteration pipe_The mineralization temperatures of ore-forming fluids vary in the range 200°C to 335°C. Thermal evolution of the fluids displays temperature profiles that first increase and then decrease with progression of mineralization processes. The majority of black-ore minerais (Groups I and II) formed during intensifying stages of hydrothermal activity, and the majority of serni-yellow-ore minerals (Group III) formed during a thermal maximum . There followed the formation of fine-grained black-ore minerals (Group IV), which interacted with barite layers during decreasing temperature phases.Oxygen and hydrogen isotope studies show that the sources of ore-forming fluids for the Kuroko­ type VMS deposits are two-fold: seawater and magmatic hydrothermal solutions, represented by the Kuroko deposits in Japan and Kuroko-type VMS deposits in Sanjiang, respectively. In the latter case the hydrothermal solutions reacted with host rocks and mixed with cold seawater percolating downward, and circulated through volcanic rocks resulting in development of alteration zones and formation of ore minerals in Kuroko-type VMS deposits."

Jan 1, 1993

By Xuanxue Mo, Zengqian Hou

"Yidun Island Arc in Sanjiang Region is one of the important Kuroko-type volcanogenic massive sulfide deposits (VMS) districts in southwestern China. Tectonically, the region is situated in the eastern portion of the Tethys orogenic belt, and is a late Triassic extensional island-arc. The island-arc underwent earlier arc construction, intra-arc rifting, later arc construction and backarc spreading during its evolution and formed a complete trench-are-basin system, i.e., the Ganzilitang suture zone, forearc basin, outer are, intra-arc rifting zone, inner arc and back-arc basin from east to west across the island-arc.Kuroko-type VMS deposits and occurrences discovered so far are limited to within the intra-arc rifting zone of the Yidun Island Arc and tend to occur in groups or clusters distributed in separate faultbound basins; e.g., Zengke, Gacun and Xiangcheng basins, in which submarine volcanic rocks, especially bimodal volcanic suites, were extensively developed. The VMS deposits formed in the waning stages of volcanic eruption in the late Triassic and are hosted in the uppermost section of acidic volcanic rocks (rhyolitic-dacitic) within a bimodal suite. The orebodies are associated with these host rocks: rhyolitic-dacitic pyroclastic rocks and exhalites and chemical sedimentary rocks.All VMS deposits in Sanjiang are of the Zn-Pb-Cu type. The architecture of the deposits is twofold, consisting of concordant lenses and layers of massive sulfides and an underlying discordant stockwork. All deposits show metal zoning. The hydrothermal alteration related to mineralization is strong and asymmetrical, and is found dominantly within the stockwork zone and host rocks surrounding the ores. There are two alteration patterns: (1) chloritization - sericitization - silicification from outer sides to core of the alteration pipe; and (2) silicification + sericitization - silicification + carbonate from the lower to upper part of the alteration pipe.The mineralization temperatures of ore-forming fluids vary in the range 200°C to 335°C. Thermal evolution of the fluids displays temperature profiles that first increase and then decrease with progression of mineralization processes. The majority of black-ore minerals (Groups I and informed during intensifying stages of hydrothermal activity, and the majority of semi-yellow-ore minerals (Group III) formed during a thermal maximum. There followed the formation of fine-grained black-ore minerals (Group IV), which interacted with barite layers during decreasing temperature phases.Oxygen and hydrogen isotope studies show that the sources of ore-forming fluids for the Kurokotype VMS deposits are two-fold: seawater and magmatic hydrothermal solutions, represented by the Kuroko deposits in Japan and Kuroko-type VMS deposits in Sanjiang, respectively. In the latter case the hydrothermal solutions reacted with host rocks and mixed with cold seawater percolating downward, and circulated through volcanic rocks resulting in development of alteration zones and formation of ore minerals in Kuroko-type VMS deposits."

Jan 1, 1993

By G B. Arehart

The Midas epithermal system is one of the larger low-sulfidation epithermal vein systems discovered in the western US in recent years, containing in excess of 3 Moz of gold (premining). The deposit is spatially and temporally related to bimodal volcanism in the Northern Nevada Rift; dates on igneous rocks (16 - 14.7 Ma) bracket the age of high grade veins (15.3 Ma). Hydrothermal alteration at Midas is typical of epithermal systems, comprising proximal potassic through distal propylitic assemblages; in contrast to many epithermal systems, Midas has minimal development of wallrock illite/sericite. Mineral assemblages are clearly zoned on the vein structures that acted as focal planes for fluid upflow. Geochemical zoning patterns also show this zoning. Metals were deposited in open-space veins as the result of boiling of hydrothermal fluids; multiple episodes of crustiform mineral deposition are documented in the vein textures. The major vein minerals include quartz, adularia, calcite, selenides and sulfides, with electrum as the primary ore mineral. REE patterns for vein material are similar to patterns for coeval rhyolites, but distinctly different from patterns of the host rocks. Stable isotope data are consistent with meteoric water as the dominant ore fluid. Combined REE and stable isotope data suggest that fluid from which the main ore-bearing stage of the veins was deposited was slightly lower pH than other stages.

Jan 1, 2005

By A. Gauthier, J .. E. Muir, M. Cormier

Falconbridge's Lac Shortt gold deposit is located in Gand Township, some 25 km north-east of Desmaraisville, The deposit was outlined in i980 by a drilling program me conducted by Falconbridge Ltd. in a joint venture with Corporation Falconbridge Copper after three years of systematic exploration by Falconbridge Ltd. in the Desmaraisville area. The gold bearing structure had previously been drilled by three other exploration companies. As based on an underground development programme conducted by Corporation Falconbridge Copper, the "in-si tu" mineral inventory to a depth of 500 metres at a cut-off grade of 3.0 g/t is estimated at 1 937 605 tonnes at a grade of 6.4 g/t (uncut) and 6.0 g/t (cut). Regionally, the stratigraphy consists of thick sequences of volcanic and volcanosedimentary rocks intruded by numerous and voluminous mafic (gabbro), felsic (granodiorite, syenite) and anorthositic intrusions. Structurally, at least two fold sets and one major fault system (E-NE) are present. Minor fault systems oriented E-NE and N-NW also occur. Mine stratigraphy can be divided into 1) - the hangingwall; 2) - ore zone; 3) - footwall. Hanging wall rocks include: a) green lapilli and blocky tuff b) transition zone c) green mica crystal tuff and d) red dolomitic tuff. Ore zone rocks include: a) bleached mafic tuff b) barren carbonates, c) pyritic dolomitic tuff (?) and d) brick-red syenite. Footwall rocks include: a) magnetic lava (so-called diorite), b) mafic lapilli and blocky tuff and c) alkali basalt, Native gold is the only gold mineral so far identified and it occurs both as free grains in gangue and as micro-inclusions in pyrite. Two geochemical groups were identified in the main rock units: 1) Alkali-rich rocks cons is ting of the ore zone and foot wall rocks and 2) Subalkaline group consisting of the hanging wall rocks. Ore analysis also shows Ba, Sr, W, Zr, REE and F enrichment in the ore zone. Footwall rocks are enriched in Na20. Present geological and geochemical data do not permit a clear interpretation of the formation for the Lac Shortt gold deposit but suggest it is a volcanic-hosted stratabound type. The bulk of the mineralization is associated with an exhalative phase following alkalic, carbonic, hydrothermal activity and part of the mineralization is associated with a late intrusive phase.

Jan 1, 1984

By J. Esson, R. A. D. Pattrick, M. K. Nimfopoulos, D. A. Polya, K. M. Michailidis

"Abstract-Economic Mn-oxide ore deposits of commercial grade occur in the Rhodope massif near Kato Nevrokopi in the Drama region, Northern Greece. The Mn-oxide mineralization has developed by weathering of continental hypogene rhodochrosite-sulphide veins. The vein mineralization is confined by tectonic shear zones between marble and metapelites, extending laterally into the marble as tabular, pod or lenticular oreshoots (up to 50 m ?? 20 m ?? 5-10 m). Supergene oxidation of the hypogene mineralization led to the formation of in-situ residual Mn-oxide ore deposits, and secondary infills of Mn-oxide ore in embryonic and well developed karst cavities.Whole rock geochemical profiles across mineralized zones confirm the role of thrusts and faults as solution passageways and stress the importance of these structures in the development of hydrothermal and supergene mineralization at Kato Nevrokopi. Three zones are recognized in the insitu supergene veins: (A) a stable zone of oxidation, where immobile elements form (or substitute in) stable oxide mineral phases, and mobile elements are leached; (B) a transitional (active) zone in which element behavior is strongly influenced by seasonal fluctuations of the groundwater table and variations in pH-Eh conditions; and (C) a zone of permanent flooding, where variations in pH-Eh conditions are minimal. Zone (B) is considered as the source zone for the karst cavity mineralization. During weathering, meteoric waters, which were CO2-rich (PCO2 ~10-3.8 to 10-1.4) and oxygenated (fO2 ~10-17 for malachite), percolated downward within the veins, causing breakdown and dissolution of sulfides and marble, and oxidation of rhodochrosite to Mn-oxides. Karst cavity formation was favored by the high permeability along thrust zones. Dissolved Mn2+ was transported into karst cavities in reduced meteoric waters at the beginning of weathering (pH~4-5), and as Mn(HCO3)2 in slightly alkaline groundwaters during advanced weathering (pH~6-8). Mn4+-oxide precipitation took place by fO2 increase in ground waters, or pH increase by continuous hydrolysis and carbonate dissolution. In the well developed karst setting, some mobility of elements occurred during and after karst ore formation in the order Na>K>Mg>Sr>Mn>As>Zn>Ba>Al>Fe>Cu>Cd>Pb."

Jan 1, 1997

By J. Esson, R. A. D. Pattrick, M. K. Nimfopoulos, D. A. Polya, K. M. Michailidis

"Economic Mn-oxide ore deposits of commercial grade occur in the Rhodope massif near Kato Nevrokopi in the Drama region, Northern Greece. The Mn-oxide mineralization has developed by weathering of continental hypogene rhodochrosite-sulphide veins. The vein mineralization is con-?ned by tectonic shear zones between marble and metapelites, extending laterally into the marble astabular, pod or lenticular oreshoots (up to 50 m x 20 m x 5-10 m). Supergene oxidation of the hypogene mineralization led to the formation of in-situ residual Mn-oxide ore deposits, and secondary infills of Mn-oxide ore in embryonic and well developed karst cavities.Whole rock geochemical pro?les across mineralized zones con?rm the role of thrusts and faults as solution passageways and stress the importance of these structures in the development of hydrothermal and supergene mineralization at Kato Nevrokopi. Three zones are recognized in the in-situ supergene veins: (A) a stable zone of oxidation, where immobile elements form (or substitute in) stable oxide mineral phases, and mobile elements are leached; (B) a transitional (active) zone in which element behavior is strongly in?uenced by seasonal ?uctuations of the groundwater table and variations in pH-Eh conditions; and (C) a zone of permanent ?ooding, where variations in pH-Eh conditions are minimal. Zone (B) is considered as the source zone for the karst cavity mineralization. During weathering, meteoric waters, which were CO2-rich (PCO2~10-3.8 to 10-1.4) and oxygenated (fO2~10-17 for malachite), percolated downward within the veins, causing breakdown and dissolution of sul?des and marble, and oxidation of rhodochrosite to Mn-oxides. Karst cavity formation was favored by the high permeability along thrust zones. Dissolved Mn2+was transportedinto karst cavities in reduced meteoric waters at the beginning of weathering (pH~4-5), and as Mn(HCO3)2in slightly alkaline groundwaters during advanced weathering (pH~6-8). Mn4+-oxide precipitation took place by fO2increase in ground waters, or pH increase by continuous hydrolysis and carbonate dissolution. In the well developed karst setting, some mobility of elements occurred during and after karst ore formation in the order Na>K>Mg>Sr>Mn>As>Zn>Ba>Al>Fe>Cu>Cd>Pb."

Jan 1, 1997

By Jr. Ensign C. O., J. W. Trammell

The two principal methods of room-and-pillar mining practiced at White Pine make it important to predict variations in the thickness and rock types of a stratum called the upper sandstone. In full column mining, the nearly barren upper sandstone occurs between two ore horizons (called upper shale and parting shale, respectively), and is mined as a part of the ore column. In general, full column mining is not practiced where excessive upper sandstone thickness causes full column ore grade to be substantially lower than parting shale ore. In parting shale mining, the upper sandstone forms the mine roof. Difficulty in predicting upper sandstone character arose because the extent and directions of its variations were not apparent in the property's diamond drilling, in which holes are spaced on 1000-ft centers. A study of sedimentary features, undertaken to improve the predictability of trends in the upper sandstone, led to an interpretation of the sedimentary environment in which the sandstone was deposited. Ripple marks, mud cracks, and cross-bedding, as well as other, less well known features, such as channel casts, flute casts, and current crescent casts, were mapped or recorded. These data, coupled with the knowledge of regional facies changes gained from studying drill core, show that the upper sandstone was deposited by a series of streams flowing northeastward over the underlying parting shale. Deposition of the lowermost bed of the upper sandstone, near the ancient shoreline, was locally preceded by erosion of the parting shale, and the greatest thicknesses of sandstone are found in channels scoured out of the parting shale. Awareness of the rather strong linear trends in the upper sandstone makes it possible to project continuous areas of thick upper sandstone through apparently isolated "highs" in the upper sandstone thickness contour map, which is based on drill-hole information. Since local exceptions to general stratigraphic trends exist, a method was also needed for esti- mating, in detail, the thickness and degree of shali-ness of upper sandstone forming the roof in active parting shale mining areas. Because locally the parting shale was thinned by erosion during the deposition of upper sandstone, parting shale thickness is inversely proportional to upper sandstone thickness. Utilizing information taken from short drill holes into the roof, curves were constructed for the correlation of parting shale thickness (measurable in the mine) with the upper sandstone total thickness, as well as the thickness of its basal member. The White Pine mine is situated in Ontonagon County, approximately 6 miles south of Lake Superior, in the Upper Peninsula of Michigan (Fig. 1). The orebody mined by White Pine Copper Co. occurs in the lowermost 20 to 25 ft of the Nonesuch formation, a series of middle- to upper-Keweenawan shales, siltstones, and sandstones. This paper discusses the solution of problems in ore grade control and mine planning arising from the presence of an essentially barren sandstone stratum within the orebody. THE OREBODY AND MINING TYPES A brief description of the orebody and mining methods is necessary to show how the upper sandstone affects mine planning and grade control. In the mine, the cupriferous zone of the Nonesuch shale is divided into three major portions, as shown in Fig. 2. Lying conformably on top of the Copper Harbor formation (or "lower sandstone") is the lower part of the orebody, the parting shale. The parting shale is overlain by the upper sandstone. On top of the upper sandstone, the basal portion (8 ft) of the upper shale is quite similar to the parting shale. Both the upper shale and parting shale are divided into a number of smaller stratigraphic units, each having a characteristic copper content, as shown by the histogram of Fig. 2. Other authors1'3 have dealt in detail with the stratigraphy and mineralogy of the orebody. However, in this article, we are concerned with the major subdivisions only, and it will suffice to note the low copper content of the upper sandstone, shown in Fig. 2. At present, two types of room-and-pillar openings are created in the orebody. In one type, called parting

Jan 1, 1964

By W. V. Swarzenski

In its effort to combat waterlogging and soil salinity, the Water and Soils Investigation Division of WAPDA (West Pakistan's Water and Power Development Authority) has carried out an extensive program of test drilling andwater sampling since 1954. Data collected during the past ten years have permitted the delineation of fresh and saline groundwater zones in the Punjab Plain. Fresh groundwater containing generally less than 500 ppm of total dissolved solids is found in wide belts paralleling the major rivers and in other areas of fresh-water recharge. Locally, fresh groundwater extends to depths of 1500 ft and more. Saline groundwater occurs down gradient from sources of recharge, particularly in the lower central parts of the interfluvial areas, and presumably underlies most of the Punjab Plain. The groundwaters of the Punjab are characterized by their evolution from calcium, magnesium bicarbonate waters near sources of recharge to waters containing a dominant proportion of sodium. The highly mineralized waters of the Punjab are generally of the sodium chloride type, whereas in the Dera Ismail Khan District, sodium sulfate waters predominate. The pattern of distribution of saline groundwater zones and the observed gradual increase in mineral content, down gradient from sources of recharge, can be explained best by a hypothesis stressing the process of evaporation from the water table and solution of minerals within the alluvial aquifer. In 1954, detailed groundwater surveys in the Punjab Plain were initiated by WASID, the Water and Soils Investigation Division of West Pakistan's Water and Power Development Authority. The investigations, undertaken under a cooperative agreement between the governments of Pakistan and the United States, were aimed at the formulation of reclamation measures to improve waterlogged and saline soils, and to assess the groundwater potential of the Punjab and other areas of West Pakistan. The nature and urgency of WASID's primary task limited the exploration of the alluvial aquifer generally to its uppermost part. About 1030 test holes drilled in 47,000 sq miles of the Punjab defined the nature of the alluvium to depths of about 600 ft and yielded data on water quality to 400 or 500 ft. A report on the hydrology of the Punjab, based on the results of these investigations was published by WASID in 1963.' The present report incorporates data obtained by WASID since 1962 in a program of deep test drilling in the Punjab and the adjacent areas of Bahawalpur and Dera Ismail Khan District, permitting the definition of fresh and saline groundwater zones to depths of 1500 ft in some areas. Groundwater in the Punjab Plain is contained in alluvial deposits, predominantly sand and silt, which extend almost everywhere to depths of 1000 ft and more. The alluvium has been deposited by the Indus River and its tributaries since late Tertiary time and is contiguous with similar deposits in India. The Indo-Gangetic Plain extends from the foothills of the Himalayas to the ancient rocks of the Peninsular Shield in central India and to the ocean. Gradients are generally very low and range from about 1% ft per mile in the upper part of the plain to less than 1 ft per mile in the south and southwest. The monotony of the alluvial plain is broken by scattered bedrock outcrops in two of the interfluvial areas, Chaj Doab and Rechna Doab. The bedrock hills are projections of the northwest-trending Delhi-Shahpur Ridge that is largely buried by alluvium. The rocks of the buried ridge, presumably of Precambrian age, are essentially impermeable and define the lower limit of the alluvial aquifer in parts of Chaj, Rechna, and Bari doabs. Elsewhere in the Punjab, there are no outcrops of other consolidated rocks and their presence below the alluvium is conjectural. The principal areas of bedrock outcrops, near Kirana and Sangla, are shown diagrammatically in Fig. 1. The movement of groundwater through the alluvial aquifer of the Punjab has been described by Green-man and others.' In most of the area, the pre-irriga-tion water table sloped from the rivers downstream and toward the central axes of the doabs, indicating that the rivers were sources of groundwater recharge. As a result of seepage from irrigation canals, water levels have risen as much as 90 ft. In 1960 they were within 5 to 15 ft of the land surface and above the

Jan 1, 1970