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By V. J. Sopuck, O. P. Lavin, Ian Nichol

"A major challenge of contemporary exploration geochemistry is the development of procedures that can locate blind mineralization or mineralization that sub-crops below a cover of transported overburden, the composition of which bears no relation to the underlying mineralization. Over the past few years, the possible existence of diagnostic geochemical features in the country rock associated with volcanogenic massive sulphide deposits has attracted increasing attention both on the local mine scale and on the regional scale. In the present investigation, the nature of the geochemistry of a number of Archean greenstone belts of the Canadian Shield is examined to determine the feasibility of distinguishing productive from non-productive areas of copper-zinc mineralization. The results indicate that productive areas are distinguishable from non-productive areas providing consideration is given to the effects of igneous differentiation on rock compositionIntroductionArchean massive sulphide deposits are an important source of copper and zinc, and to a lesser extent silver and gold, particularly in Canada. As in the case of most other forms of mineralization, there is a continual need to develop new techniques that will improve the chances of success in the search for these deposits. The majority of Archean areas in the northern latitudes are overlain by a variable cover of glacial overburden. Considerable progress has been made in the development of new geochemical exploration techniques for use in glaciated terrain, based on the detection of anomalous dispersion in the glacial overburden. In certain situations, however, as in the search for blind deposits or in areas covered by glaciolacustrine deposits, overburden geochemistry offers little hope for success. In the case of massive sulphide deposits, one possible solution may lie in the detection of anomalous geochemical signatures in the bedrock. Recognizing this possibility, attention has been directed to the investigation of the nature of lithogeochemical dispersion associated with massive sulphide deposits on both regional and local scales, to establish the potential of lithogeochemistry as an aid in the search for these deposits."

Jan 1, 1980

Ancient volcanogenic Cu-Zn-Pb-Ag-Au massive sulfide ores commonly have associated with them along strike and in the immediate hanging wall a distinctive sediment that is thin, usually cherty and metal enriched, and generally referred to as an "exhalite horizon" or "tuffaceous exhalite". Typical examplks include the 13 Ma tetsusekiei of the Kuroko deposits of Japan (Kalogeropoulos and Scott, 1983, Econ. Geol.) and the 2700 Ma contact tuffs of Noranda, Canada (Kalogeropoulos and Scott, 1989, Can. J. Earth Sci.) and Key Tuffite of Mattagami, Canada (Liaghat and McLean, 1992, Explor. Min. Geol.). Attempts to use trace element distributions as lithogeochemical guides to ore have been largely unsuccessful. Exhalites have been considered to be the products of seafloor hydrothermal activity that is peripheral to the main ore-producing vents. However, large actively-forming polyrnetallic sulfide deposits at the Explorer mid-ocean basalt spreading ridge (1 850 m depth) in the NE Pacific and the eastern Manus back-arc dacitic spreading center (1650 m depth) in the western Pacific have demonstrated that the exhalite horizons are more likely produced by fallout of particulates from the main hydrothermal plume. In a typical hydrothermal plume, grains of >27 µm represent up to 97% of the mass (although only 2% of the population) of the particulates and are calculated by Stokes equations to fall from the plume to the seafloor within a few krn of their source. The particles are primarily composed of anhydrite, barite, amorphous silica, iron oxyhydroxides and metal sulfides and oxides. Plumes are subject to bottom currents which push them in preferred directions, just like smoke plumes in the atmosphere are subject to the vagaries of wind direction. Bottom currents in the deep ocean can be 50 m/min or

Jan 1, 1993

By P. Trudel, M. A. . Cloutier

This lithogeochemical study demonstrates that the Gilman and Blondeau Formations in the Chibougamau area belong to a subalkaline suite of tholeiitic affinity poor in potassium. The Gilman Formation is composed mostly of basalts, with subordinate andesites and rare dacites, while the Blondeau Formation comprises all lithologies of the basalt-andesite-dacite-rhyodacite-rhyolite ensemble. Both AFM and Harker variation diagrams show that all these rocks originated by differentiation from the same magma reservoir, and are related to one volcanic episode, This study did not, however, identify hydrothermal alteration zones useful for regional geochemical prospect ion.

Jan 1, 1984

By Michel Mellinger

This paper presents preliminary results of a project aimed at obtaining a better understanding of the genesis of gold mineralization in northern Saskatchewan using lithogeochemistry. The properties sampled were: Weedy Lake (B Zone), Waddy Lake (Komis Zone) and Wedge Lake (Twin Zone) in the La Range belt, and the Rio mine in the Flin Flon area. Although the three vein-type deposits rudied here (Weedy Lake. Waddy Lake, Rio deposit) occur in different geological situation . a common gold deposition mechanism appears to have been active at all three location . Hydrothermal fluids carrying sulphur in solution in exces of gold thio-complexes moved through fractured host-rocks until they reached a site where pyrite precipitation wa triggered. As pyrite precipitated, the a/ aAu activity ratio of the fluid decreased. until a critical thre hold was reached and gold thio-complexe were de tabilized . resulting in the co-precipitation of gold and pyrite. The conditions triggering the precipitation of pyrite appear to have been: the abundance of iron in host-rock ~ilicates at Waddy Lake. and temperature decrease upon the reaching of structural trap~ at both Weedy Lake and the Rio deposit. with additional involvement of carbonatizationrelated reactions between fluid and host-rocks for the latter. In addition to pyrite precipitation , potassic alteration of the mafic metavolcanics is observed at Waddy Lake. while at the Rio deposit, the extensive carbonatization of the host-rocks i coupled with the deposition of chlorite that may have been remobilized from the altered mafic host rocks. In both the B Zone at Weedy Lake and the Komis Zone at Waddy Lake, a di tinct vanadium signature give some clue about the direction in which the hydrothermal fluids have moved . and the interpretation made is con istent with the geological ituation in either case. As for the Wedge Lake deposits, the distinct base metals-precious metals a sociation within a sulphide-facies iron formation confirm the volcanic exhalative origin of this gold mineralization .

Jan 1, 1986

By Charles Merguerian

In medium- to high-grade metamorphic terrains such as found in New York City(NYC), rock mass texture and mineralogy are important factors in predicting TBM penetration destiny. Integration of data from over two decades of traditional field and tunnel mapping suggest that hard-rock TBM penetration in the NYC area depends upon textural, mineralogic, and structural control. The bedrock of NYC consists of many different lithologic units of varying age, composition, texture, and metamorphic grade including many varieties of intrusive rock. In addition, brittle faults of numerous orientations cut the polydeformed crystalline bedrock, producing zones of highly fractured and disturbed ground and high water inflows. Pre-bid compilation of published bedrock data, drill core analysis by geologists to establish lithologic and mineralogic trends, integrated surface geologic mapping along a proposed alignment, and targeted petrographic and geotechnical investigations to characterize the rock mass conditions together constitute an important prelude to successful subsurface bidding and tunneling. A carefully planned program of as-built geological mapping, structural analysis, fracture class mapping, and monitoring of machine performance data provide important information for adjusting to changed conditions. In complex terrains, a clear understanding of the structural geology of any proposed tunnel line is the simplest and most cost-effective method to mitigate losses encountered during TBM tunneling.

Jan 1, 2005

By D. A. Lindsey

Gravel lithology affects the quality of aggregate because different rock types in gravel have different physical and chemical properties. The lithologic composition of alluvial gravel reflects the composition of its source terrane and the variable effects of weathering and transport on each rock type. This report discusses lithologic controls on aggregate quality in the mountain-front environment of the Colorado Front Range. Lithologic controls on aggregate quality of gravels were evaluated using pebble count data. Gravel lithology along the Front Range shows both temporal and regional variation. The principal variable in gravel lithology is quartz plus quartzite, of which quartzite is commonly more abundant. Large quantities of metaquartzite derived from the mountain front southwest of Boulder, Colo., were dispersed northeastward during deposition of the oldest Front Range gravels. Average quartz plus quartzite is greatest in the oldest gravels. Aggregate quality is probably enhanced by large quantities of quartzite. Abundant volcanic rocks in gravel may enhance aggregate quantity, but such occurrences are local in extent. Abundant sedimentary rocks in gravel, mainly sandstone near the mountain front, may decrease aggregate quality.

Jan 1, 2002

By Jr. Abel

Subsidence is controlled by a complex combination of mining and geologic factors. For example, a world-wide compilation of data shows that, as the percentage of shale in the overying rock mass decreases and the amount of sandstone increases, the angle of draw (and the area affected by subsidence) decreases. Limestone in the overburden appears to cause as much as a three-fold decrease in the angle of draw compared to a like amount of sandstone. Increased amounts of sandstone were accompanied by a greater surface subsidence relative to the mining height. The total thickness of overburden did not appear to influence the subsidence magnitude above super-critical panels. The greater the thickness extracted the smaller percentage of that thickness that shows up at the surface as subsidence. The greater the percent of the seam extracted, the greater the subsidence reaching the surface. The maximum subsidence above room and pillar panels is dependent on the pillar height and minimum width as well as the other factors listed.

Jan 1, 1980

By J. F. Abel, F. T. Lee

Subsidence is controlled by a complex com¬bination of mining and geologic factors. For example, a compilation of worldwide data shows that, as the percentage of shale in the overlying rock mass decreases and the amount of sandstone increases, the angle of draw (and the area affected by subsidence) decreases. Limestone in the over¬burden appears to cause a more than twofold decrease in the angle of draw compared to a like amount of sandstone. Increased amounts of sandstone were accompanied by a greater surface subsidence relative to the mining height. The total thickness of overburden did not appear to influence the subsidence magnitude above super-critical panels. The greater the thickness extracted, the smaller percentage of that thickness shows up at the surface as subsidence. The greater the percent of the seam extracted, the greater the subsidence reaching the surface. The maximum subsidence above room-and-pillar panels de¬pends on the pillar height and minimum width as well as the other factors listed.

Jan 1, 1984

By Edward J. Walter

Vibration control is affected by many factors which are difficult to isolate and evaluate. Occasionally a circumstance occurs in which one factor appears to predominate and its effects can be evaluated. Changing rock characteristic or lithologic variation is one of these factors or parameters. In a recent seismic monitoring project, lithologic variation in the form of hard lenses occurring suddenly and randomly in the rock to be excavated caused sudden and large increases in vibration level. Data are presented to illustrate these effects, and procedures used to control these effects are described.

Jan 1, 1981

By Pierre J. Goossens

Since Guild 1 and Snelgrove 2 attracted our attention to the relationships between certain endogenic ore deposits and plate boundaries, an abundant flow of papers appeared in the metallogenic literature concerned with this problem and its application to mineral exploration. Some of the papers only speculate with the formation of specific type of ore deposit 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 Other papers are more concerned with genetic and structural relationships between plate tectonics and mineralization 13, 14, 15, 16, 17, 18, 19, 20 They are philosophical, in that they are generalized and refer to no specific area. Yet it is true that a large part of the world mineral potential is concentrated at the convergence of oceanic and continental plates, for example, around the Pacific. Therefore, the interaction of two plates by either subduction, obduction or slippage likely has an important role for the genesis and/or the (structural) control of these "orogenic" ore deposits. If subduction is the driving mechanism for the generation of igneous rocks 21, 22 and endogenic ore deposits 18, volcanic activity and the nature of volcanic products certainly are the major geologic processes and events to be tested. Fonteilles 23 and Alsac 24 have already emphasized the important relationship between mineralization and the talc-alkaline affinity of the volcanics. The Andean orogen is one of the best areas for testing such genetic relationships. Rich and varied endogenic and volcanogenic ore deposits occur there and plate interaction is still active.

Jan 1, 1975

By Pierre J. Goossens

The coastal Cordillera around the Panama basin is made up of a Cu-rich tholeiitic volcanic belt representing either immature, late Mesozoic, island arc, or oceanic ridge. The same belt is exposed (uplifted) along the western slope of the Cordillera Occidental of Ecuador and Colombia. Ni-lateritic, Cr-podiform, and Pt-(Au) placer deposits are formed there after or within ultramafic bodies of oceanic association. Younger calc-alkaline igneous activity provided the mechanism for porphyry copper and associated ore formation. This Cu (+Mo) mineralization occurs along a narrow belt exposed by the erosion of the volcanic cap. Ag-Pb-Zn(-Au) and Hg volcanogenic mineralizations occur within the calc-alkaline belt, but slightly eastward and only above the copper belt. To the east and in the Venezuelan Andes, Paleozoic and older sediments, volcanics, and metamorphics contain volcanogenic massive sulfide, Pb-Zn, Au, and Cu sedimentary and vein deposits, and sedimentary iron ore and phosphate. The Cenozoic Cu, Ni-Pt-Cr and a portion of Ag-Pb-Zn, Hg, and Au mineralizations occur within or just above the oceanic basement whereas the eastern- most Cenozoic Ag-Pb-Zn mineralizations occur within and above a pre-Cenozoic sialic basement. This continental crust is the northern extension of the Peru-Chilean Andes where no oceanic crust has been preserved, however. Cenozoic metallogeny and subduction relationships are unclear in the Northern Andes. Yet strong structural volcanogenic ore controls exists apparently due to deep strike-slip movement between two plates.

Jan 1, 1977

By Luc Harnois, Gabriel Voicu, Marc Bardoux, Robert Crépeau

"Abstract-Detailed petrographical and geochemical studies have been carried out on the igneous and sedimentary rocks in the Omai area, part of the Paleoproterozoic Barama-Mazaruni greenstone belt, Guyana. The stratigraphic succession at Omai begins with basalts, associated with mafic-ultramafic intrusives and poorly-sorted conglomerates; these are overlain by andesites and quartzfeldspar porphyries, with pelites and tuffaceous sediments at the top. The volcanic-sedimentary succession was intruded by a quartz-monzodioritic stock (Omai stock) and granophyric rhyolite dikes. Several generations of mafic dikes were intruded discontinuously from the Mesoproterozoic to the Permo-Triassic. Volcanic rocks range in composition from subalkaline basalt to high-silica rhyolites, with a gap between 60% to 70% SiO2, which suggests the suite is bimodal. Major, trace, and rare earth element criteria were used to subdivide the rocks into tholeiitic and calc-alkaline types. The tholeiitic rocks are characterized by flat to moderately sloping chondrite-normalized REE patterns. On the basis of immobile trace-element ratios, the tholeiitic mafic rocks from Omai have characteristics of immature intra-oceanic island arcs, or of E-MORB basalts affected by a strong arc signature, as is commonly reported for back-arc basin basalts. The andesites, quartz-feldspar porphyries, rhyolites and quartz monzodioritic stock are calc-alkaline, with strongly sloping REE patterns, enrichments in the large-ion lithophile elements, and depletions in the heavy REE and high-field-strength elements, features which are typical of more mature island-arc settings.At Omai, two types of gold-bearing veins can be distinguished: vein sets (± stockworks) and tension veins, both post-dating the regional metamorphic peak at the level they were emplaced. The relationship between the gold mineralization and its host lithologies does not seem to be genetic. Rather, the emplacement of mineralization was strongly influenced by the rheological contrasts between the intrusive/subvolcanic bodies and the volcanic/sedimentary country rocks. These contrasts helped to focus the regional stress upon the more competent intrusive subvolcanic bodies, resulting in brittle fracturing, and therefore in greatly enhanced permeability to hydrothermal fluids. The Omai gold mineralization can be classified as late tectonic, with its emplacement controlled by the last brittle to brittle-ductile stages of the Trans-Amazonian orogeny."

Jan 1, 1997

By Gabriel Voicu, Harnois Luc, Marc Bardoux, Robert Crépeau

"Detailed petrographical and geochemical studies have been carried out on the igneous and sedimentary rocks in the Omai area, part of the Paleoproterozoic Barama-Mazaruni greenstonebelt, Guyana. The stratigraphic succession at Omai begins with basalts, associated with ma?c-ultrama?c intrusives and poorly-sorted conglomerates; these are overlain by andesites and quartz-feldspar porphyries, with pelites and tuffaceous sediments at the top. The volcanic-sedimentary succession was intruded by a quartz-monzodioritic stock (Omai stock) and granophyric rhyolitedikes. Several generations of ma?c dikes were intruded discontinuously from the Mesoproterozoicto the Permo-Triassic. Volcanic rocks range in composition from subalkaline basalt to high-silicarhyolites, with a gap between 60% to 70% SiO2, which suggests the suite is bimodal. Major, trace, and rare earth element criteria were used to subdivide the rocks into tholeiitic and calc-alkaline types. The tholeiitic rocks are characterized by ?at to moderately sloping chondrite-normalized REE patterns. On the basis of immobile trace-element ratios, the tholeiitic ma?c rocks from Omai have characteristics of immature intra-oceanic island arcs, or of E-MORB basalts affected by a strong arcsignature, as is commonly reported for back-arc basin basalts. The andesites, quartz-feldspar porphyries, rhyolites and quartz monzodioritic stock are calc-alkaline, with strongly sloping REE pat-terns, enrichments in the large-ion lithophile elements, and depletions in the heavy REE and high-?eld-strength elements, features which are typical of more mature island-arc settings.At Omai, two types of gold-bearing veins can be distinguished: vein sets (± stockworks) and tension veins, both post-dating the regional metamorphic peak at the level they were emplaced. The relationship between the gold mineralization and its host lithologies does not seem to be genetic. Rather, the emplacement of mineralization was strongly in?uenced by the rheological contrasts between the intrusive/subvolcanic bodies and the volcanic/sedimentary country rocks. These con-trasts helped to focus the regional stress upon the more competent intrusive subvolcanic bodies,resulting in brittle fracturing, and therefore in greatly enhanced permeability to hydrothermal ?uids.The Omai gold mineralization can be classi?ed as late tectonic, with its emplacement controlled by the last brittle to brittle-ductile stages of the Trans-Amazonian orogeny."

Jan 1, 1997

By D Craw

Interactions between structure and lithology in the Hyde-Macraes Shear Zone controlled the style of gold mineralisation at the Macraes mine. Large volumes of rock in some mine pits have most gold disseminated in hydrothermally altered schist, rather than in quartz veins. Mineralisation was initiated in the latter stages of metamorphism. Pods of massive schist rich in quartz and feldspar are surrounded by more fissile schist consisting of interlayered micaceous and quartzofeldspathic schist. Later shears have been partly controlled by the micaceous schist, and anastomose around pods of more massive schist. Micaceous schist was replaced by pyrite and arsenopyrite, accompanied by recrystallisation of phengitic muscovite under lower greenschist facies conditions. Gold occurs in sulfides and with microcrystalline quartz formed during minor silicification. Massive schist is locally mineralised along sulfidic microshears which have phengitic muscovite largely illitised under sub-greenschist facies conditions. Mineralised massive and micaceous schists were overprinted by cataclastic shears, with addition of graphite and more sulfides. Mineralisation occurred during a transition from ductile to brittle deformation regimes as the schist was uplifted in the late Jurassic.

Jan 1, 2004

East Otago gold deposits are hosted in Otago Schist that is the metamorphosed equivalent of Permian-Triassic Torlesse terrane greywackes. Relatively undeformed Torlesse sequences in Canterbury have <l m - 50 m bedding, with c. 500 m - l km and c. three kilometre scale units, typically either: 1) thick-bedded, massive, sandstones; 2) thin-bedded sandstone-argillite flysch; or 3) siltstone- or argillite-dominated units. Such lithological layering in Otago was intensely folded, deformed, and overprinted by metamorphic fabrics during Jurassic-Cretaceous regional metamorphism. Although primary sedimentary structures can no longer be recognised, a æghostÆ lithological variation is still present in Otago represented by psammitic (sand-derived), interlayered (sandstone-siltstone derived) and pelitic (siltstone-mudstone derived) schist. Lithological æunitsÆ in the schist are typically either 20 100 m or c.1 - 2 km thick, and are oblique to faults and shears hosting gold mineralisation at Macraes, Barewood, Nenthom, and Oturehua. Lithological variations and folds in lithological units are important in the along-strike distribution of gold in these deposits, and in the development of relatively high-grade pods and shoots at l00 m - 1.5 km scales. Ramps, flats and step-overs (known to be locally important for controlling mineralisation) are commonly located at lithological boundaries, presumably by local refraction of faults or shear zones as they propagated through folded stratigraphy. The various lithologies have also responded differently to deformation, causing variations in permeability that affected the penetration of mineralising fluids. Mapping lithological variations in barren host-rocks, either directly+ by fieldwork or indirectly by aerial geophysics, is a key to understanding and predicting the distribution of gold at mine and deposit scales.

Jan 1, 2001

By J. Peck, M. J. Scobie, M. D. Pollitt

"IntroductionOne aspect of current research in the Canadian Centre for Automation and Robotics in Mining (CCARM) involves the automatic identification of different rock types based on particular drill performance parameter responses. In this paper, the four drill performance parameters of torque, pulldown pressure, rotary speed and penetration rate, were measured from an instrumented rotary blasthole drill during field investigations undertaken at the Fording River Mine, Elkford, British Columbia. The variations in these parameters were subsequently correlated with the corresponding rock types using the results from gamma, neutron and core logs in the same or adjacent boreholes. Work to date has sought to understand the relationships between drilling performance parameter variation and rock properties. Using the results of these studies, the present research is aimed at developing techniques whereby classical statistical pattern recognition methods are applied to drill data to permit the discrimination of different rock units. A monitoring system incorporating such a capability would greatly enhance the quality and amount of geological information on a per borehole basis while drilling. This data in tum could be used economically and directly towards explosive loading, geological exploration and reserve estimation. Background and PhilosophyThis work is an extension of equipment monitoring studies at the Fording River Mine. At this site over a two-year period, 5180 m of data was acquired on an instrumented Bucyrus-Erie 60R drill during routine production blasthole drilling. Throughout these studies, a 311mm diameter S8M Security tungsten-carbide tricone bit was used. The mine, located in southeast British Columbia, is a large-scale, open pit coal operation. The means of excavation revolves around a drill-blast-muck cycle and employs a standard shovel-truck system of transport. Four main rock types are present: sandstone, siltstone, mudstone and coal, with average compressive strengths ranging from 10 MPa to 150MPa respectively (peck 1989). However, based on the field studies, very few differences in terms of strength and compositional properties were seen between the sandstones and siltstones at the site. Therefore, they are referred to as sandstone/siltstone in all further discussions."

Jan 1, 1991

By M. M. Swan

A stratiform gold occurrence of Precambrian age located 20 miles southeast of Prescott, Arizona, within the Agua Fria Mining District, displays chemical, mineralogical, structural and lithological patterns indicative of a distal, exhalative volcanogenic environment. Metavolcanic and metasedimentary rocks of the Proterozoic Yavapai Series (1775-1820 m.y.) host the mineralization and are'characterized by greenschist grade metamorphism, steeply-plunging penetrative folds and steeply-dipping schistosity. Mineralization is confined to a 100m thick stratigraphic section that is comprised of a series of thin auriferous massive sulfide beds and intercalated schist .containing disseminated sulfides. The mineralization extends more than 4km along strike. Coincident with, and largely confined to the mineralized strata, are anomalous amounts of As, Sb, Cu, Pb, Zn and Ag and associated silicification, sericitization and carbonatization. This exhalative mineralized system is interpreted to have been deposited in a paleo topographic low on the distal flank of a submarine rhyolite dome and to represent the final episode of a Precambrian volcanic cycle.

Jan 1, 1981

By V Salamakha, K Tang, G Si, J Oh, X Wu, Z Yu

The development of machine learning (ML) algorithms has led to promising advances in lithology classification from geophysical logs, which is indispensable in various underground engineering applications. Due to the resolution and availability of logging data, ML models can recognise lithology change in a definitive form at a fine scale (0.01 m). While the results from previous models indicated promising performance in the classification, the robust capability of generalising lithology prediction to unseen data may not be true for those models due to: (1) data bias caused by borehole selections, and (2) logging data mismatches among boreholes. To this end, this paper aims to investigate the generalisability of ML models and seek potential improvements. Four ML models were selected to be trained on single reference boreholes to test the other (as unseen) in the same region, which includes Support Vector Classifier (SVC), Random Forest (RF), eXtreme Gradient Boosting (XGBoost) and Residual Neural Network (ResNet10). The data set involves 11 boreholes from a coalmine in north-western Bowen Basin (Queensland, Australia): density, gamma ray, neutron, and sonic logs are selected as inputs. Additionally, a data adaptation method is applied for better generalisability. The results show that there is an accuracy trade-off between the same borehole and unseen boreholes across the models. It also indicates a 16–43 per cent reduction in model performance when generalising the predictions (in marco-F1 score), while the adapted data sets can contribute to a around 12 per cent improvement. This study provides a fundamental understanding of the model generalisability when using a single borehole, essential for further correlating boreholes for regional lithology classification; the adaptation method can improve the generalised accuracy, and reduces the labour to label lithology, which facilitates the identification of gas storage mechanisms, geological/geophysical modelling, and stratigraphic analysis.

Sep 1, 2024

By L. S. Panyity

THE State of Ohio is among the pioneers in the production of oil and gas. Numerous anticlinals, such as the Macksburg, Cow Run and Newport, have been thoroughly developed, and the pools found in connection with them are quite in accord with the structural theory. Numerous oil and gas pools found in the Berea sand, however, demand a different explanation. The study of these pools belongs to the sub-surface geologist, as it is possible to understand the factors controlling "off-structure" accumulations only after a careful study of well records. By carefully analyzing the various 'conditions over a large territory, it is possible to understand the otherwise meaningless mass of data that one may have at hand, and put it into tangible shape, from which various conclusions may be drawn. The territory here discussed includes Belmont, Guernsey, Muskingum, Noble, Monroe, Morgan, Washington, Athens and Meigs counties, containing the majority of the prolific oil and gas pools of the Carboniferous system in southeastern Ohio. The general dip of the strata is to the southeast, the entire territory lying on the northwestern flank of the Appalachian geosyncline. The best known oil- and gas-producing horizon in the territory is the Berea sand, which lies near the lower part of the Mississippian, with the Sunburry shales (the coffee-shales of the driller) above, and the Bedford shales below it. The Bedford is underlain by the thick Ohio shales. The Ohio and Bedford contact is considered to be the dividing line between the Carboniferous and Devonian systems. The Berea is one of the most persistent of recognizable oil and gas horizons; its outcrop has always been found in its expected place, and it has always been penetrated whenever the drill went deep enough. It is not expected, however, even of the most uniform formations, that no lithological variations should occur, and the Berea is no exception. Nevertheless, there appears to be a certain regularity in its variation, the main features of which directly affect the accumulation of petroleum.

Jan 8, 1918

By Thon T. Gin

The lithologic, mineralogic, and magnetic beneficiation characteristics of the iron formation at U. S. Steel's Atlantic City Ore Mine, Fremont County, Wyoming, have been determined. The iron formation averages about 30 percent Fe content, and varies from 125 feet to about 500 feet in thickness. It is composed of interbedded magnetite-rich quartzites, magnetite-quartz-amphibole schists, and amphibole-chlorite schists. Quartz, actinolite-tremolite, chlorite, and magnetite are the essential mineral constituents. These rocks are differentiated into four major ore types on the basis of their relative quartz and amphibole content. The iron content of the magnetic concentrate decreases and the silica content increases with decreasing grain size and increasing amphibole content in each ore type at the same fineness of grind. Criteria were developed to enable the mine operator to recognize the ore types and to blend them to produce a more uniform concentrator feed. This results in less variation in product quality and requires fewer changes in operating conditions-in the concentrator.

Jan 1, 1965