Laterally extensive modified placer gold deposits in the Paleoproterozoic Mississagi Formation, Clement and Pardo Townships, Ontario

2011 ◽  
Vol 48 (5) ◽  
pp. 779-792 ◽  
Author(s):  
D.G.F. Long ◽  
T. Ulrich ◽  
B.S. Kamber
Keyword(s):  
Massive Sulfide ◽  
Gold Deposits ◽  
Low Flow ◽  
Braided Rivers ◽  
Valley Fill ◽  
Potential Source ◽  
Lake Formation ◽  
Lateral Extent ◽  
Topographic Relief ◽  
Depositional Elements

Local gold concentrations are found in laterally extensive pyrite-bearing, framework-supported, cobble and boulder conglomerates in the basal 30 m of the Mississagi Formation in the south eastern part of the Huronian outcrop belt. These were deposited as part of a valley-fill succession, in shallow gravel-bed braided rivers with local hyperconcentrated flows. The basal contact with underlying Archean psammites is typically highly irregular and shows no obvious sign of weathering suggesting that deposition took place soon after retreat of the glaciers responsible for deposition of the Ramsey Lake Formation. Highest gold concentrations are associated with moderately well-sorted medium to large pebble conglomerate that show some signs of reworking during low flow events. Depositional elements are typically lenticular and of limited lateral extent. Unlike the older pyritic quartz-pebble conglomerates at the base of the Matinenda Formation in the Elliot Lake and Blind River areas, these conglomerates contain no uraninite and are polymict with material derived from a highly restricted catchment area with marked local and regional topographic relief. Porous detrital allogenic pyrite and euhedral post-depositional pyrite have overlapping, generally positive δ34S values, indicating a closed system during diagenesis and metamorphism. The presence of biotite-enriched rims on many of the metavolcanic and metasedimentary clasts in the conglomerates suggests that gold was partly leached from the allogenic pyrite grains at the peak of the Penokean Orogeny at 1.85–1.5 Ga. The potential source of the Au-bearing detrital allogenic pyrite appears to be an as yet undiscovered Archean volcanic-hosted massive sulfide (VHMS) deposit located 1 to 8 km north of the deposit.

Gold Exploration and Potential of the Appalachian Piedmont of Eastern Alabama

SEG Discovery ◽  
2013 ◽  
pp. 1-17
Author(s):  
Jim Saunders ◽  
Mark Steltenpohl ◽  
Robert B. Cook
Keyword(s):  
Massive Sulfide ◽  
Gold Deposits ◽  
Southern Appalachians ◽  
Sulfide Deposits ◽  
Gold Exploration ◽  
Geochemical Association ◽  
Carolina Slate Belt ◽  
Appalachian Piedmont ◽  
Metamorphic Terranes ◽  
Exploration Activity

ABSTRACT: The discovery and production of gold from epithermal and volcanogenic massive sulfide deposits in the Carolina slate belt of the southern Appalachians perhaps have overshadowed the gold potential of orogenic gold deposits in relatively higher grade metamorphic terranes of the southern Appalachian Piedmont. There has been a limited amount of exploration in the non-Carolina slate belt southern Appalachians since the early 1980s. Here we describe some of the recent exploration activity and geology of gold occurrences in the most productive part of the Alabama Piedmont, including the Goldville and Devil’s Backbone districts. In this area, there is a strong geochemical association of gold and arsenic in bedrock, saprolite, and soils, which reflects the mineralogical association of gold with arsenian pyrite and arsenopyrite in mineralized zones.

Subduction, mantle metasomatism, and gold: A dynamic and genetic conjunction

2019 ◽  
Vol 132 (7-8) ◽  
pp. 1419-1426 ◽  
Author(s):  
David I. Groves ◽  
Liang Zhang ◽  
M. Santosh
Keyword(s):  
Subduction Zones ◽  
Massive Sulfide ◽  
Mantle Metasomatism ◽  
Gold Deposits ◽  
Genetic Models ◽  
Dynamic Factor ◽  
Convergent Margins ◽  
Copper Gold ◽  
Orogenic Cycle ◽  
Fluid Release

Abstract Global gold deposit classes are enigmatic in relation to first-order tectonic scale, leading to controversial genetic models and exploration strategies. Traditionally, hydrothermal gold deposits that formed through transport and deposition from auriferous ore fluids are grouped into specific deposit types such as porphyry, skarn, high- and low-sulfidation–type epithermal, gold-rich volcanogenic massive sulfide (VMS), Carlin-type, orogenic, and iron-oxide copper-gold (IOCG), and intrusion-related gold deposits (IRGDs). District-scale mineral system approaches propose interrelated groups such as porphyry Cu-Au, skarn Cu-Au-Ag, and high-sulfidation Au-Ag. In this study, the temporal evolution of subduction-related processes in convergent margins was evaluated to propose a continuum of genetic models that unify the various types of gold deposits. At the tectonic scale of mineral systems, all hydrothermal gold deposits are interrelated in that they formed progressively during the evolution of direct or indirect subduction-related processes along convergent margins. Porphyry-related systems formed initially from magmatic-hydrothermal fluids related to melting of fertile mantle to initiate calc-alkaline to high-K felsic magmatism in volcanic arcs directly related to subduction. Formation of gold-rich VMS systems was related to hydrothermal circulation driven by magmatic activity during rifting of oceanic arcs. Orogenic gold deposits formed largely through fluids derived from devolatilization of the downgoing slab and overlying sediment wedge during late transpression in the orogenic cycle. Carlin-type deposits, IRGDs, and some continental-arc porphyry systems formed during the early stages of orogenic collapse via fluids directly or indirectly related to hybrid magmatism from melting of lithosphere that was metasomatized and gold-fertilized by earlier fluid release from subduction zones near margins of continental blocks. The IOCGs were formed during postorogenic asthenosphere upwelling beneath such subduction-related metasomatized and fertilized lithospheric blocks via fluid release and explosive emplacement of volatile-rich melts. Thus, importantly, subduction is clearly recognized as the key unifying dynamic factor in gold metallogenesis, with subduction-related fluids or melts providing the critical ore components for a wide variety of gold-rich deposit types.

scholarly journals A review of methods for measuring groundwater–surface water exchange in braided rivers

2019 ◽  
Vol 23 (10) ◽  
pp. 4397-4417 ◽  
Author(s):  
Katie Coluccio ◽  
Leanne Kaye Morgan
Keyword(s):  
Surface Water ◽  
Water Exchange ◽  
Global Scale ◽  
Low Flow ◽  
Hyporheic Exchange ◽  
European Alps ◽  
Braided Rivers ◽  
River Bed ◽  
Multi Method Approach ◽  
Remote Sensing Techniques

Abstract. Braided rivers, while uncommon internationally, are significant in terms of their unique ecosystems and as vital freshwater resources at locations where they occur. With an increasing awareness of the connected nature of surface water and groundwater, there have been many studies examining groundwater–surface water exchange in various types of waterbodies, but significantly less research has been conducted in braided rivers. Thus, there is currently limited understanding of how characteristics unique to braided rivers, such as channel shifting, expanding and narrowing margins, and a high degree of heterogeneity affect groundwater–surface water flow paths. This article provides an overview of characteristics specific to braided rivers, including a map showing the regions where braided rivers are mainly found at the global scale: Alaska, Canada, the Japanese and European Alps, the Himalayas, Russia, and New Zealand. To the authors' knowledge, this is the first map of its kind. This is followed by a review of prior studies that have investigated groundwater–surface water interactions in braided rivers and their associated aquifers. The various methods used to characterise these processes are discussed with emphasis on their effectiveness in achieving the studies' objectives and their applicability in braided rivers. We also discuss additional methods that appear promising to apply in braided river settings. The aim is to provide guidance on methodologies most suitable for future work in braided rivers. In many cases, previous studies found a multi-method approach useful to produce more robust results and compare data collected at various scales. Given the challenges of working directly in braided rivers, there is considerable scope for the increased use of remote sensing techniques. There is also opportunity for new approaches to modelling braided rivers using integrated techniques that incorporate the complex river bed terrain and geomorphology of braided rivers explicitly. We also identify a critical need to improve the conceptual understanding of hyporheic exchange in braided rivers, rates of recharge to and from braided rivers, and historical patterns of dry and low-flow periods in these rivers.

Evidence from lead isotopes regarding the genesis of ore deposits in the Chibougamau region, Quebec

1981 ◽  
Vol 18 (4) ◽  
pp. 708-723 ◽  
Author(s):  
R. I. Thorpe ◽  
Jayanta Guha ◽  
Jules Cimon
Keyword(s):  
Lead Isotopes ◽  
Spatial Association ◽  
Massive Sulfide ◽  
Gold Deposits ◽  
Ore Deposits ◽  
Carbonate Sediments ◽  
Sulfide Deposits ◽  
Copper Gold ◽  
Genesis Of Ore Deposits ◽  
Isotope Analyses

Twenty-three lead isotope analyses are reported for massive sulfide deposits, the main copper–gold shear zone deposits in anorthosite of the Doré Lake complex, and two gold deposits, all in Archean terrane, in the Chibougamau district. Five analyses were also obtained for lead occurrences in Proterozoic carbonate sediments in the Mistassini Basin.Galenas from the Coniagas and Lemoine deposits of volcanogenic massive sulfide type, from the Taché Lake deposit of possibly the same type, from the Norbeau and Ayrhart gold properties, and one from within the Opemiska mine, have Archean compositions. Of these, the Lemoine, Norbeau, and Opemiska mine galenas are slightly younger than the others or were contaminated during later deformation and (or) metamorphism.Analyses for the main Cu–Au deposits generally form a cluster, although the spread in 206Pb/204Pb ratios is significant and three analyses for the Copper Rand deposit, in particular, are distinct from data for the other deposits. One interpretation is that the data, in combination with the Archean analyses, define a secondary isochron reflecting a primary age of Archean deposits and rocks at 2735–2800 Ma and a secondary event, including genesis of the Cu–Au ores, at 2240–2160 Ma. Additional evidence for a metamorphic–plutonic(?) event at about 2200 Ma has been provided by previous paleomagnetic studies. One galena from the Opemiska deposit appears to have had uranogenic lead added at 1735–2075 Ma. Three analyses of galena from the Campbell (Merrill) pit are anomalous or indicate they were formed at 162–300 Ma, and it is suggested they may have resulted from multiple episodic additions of ambient rock lead to galena originally deposited at about 2200 Ma.Two new analyses, together with four older values, for Mistassini Basin lead occurrences define a possible secondary isochron that may indicate an integrated source age of 2655 or 2940 Ma at mineralization ages of 2100 and 1700 Ma, respectively. This secondary isochron is very poorly defined because three other new analyses plot above the line.This study suggests that further geochronological investigation of the Cu–Au orebodies, and of felsic dykes that occur in many cases in close spatial association with them, should be undertaken.

scholarly journals Critical role of caldera collapse in the formation of seafloor mineralization: The case of Brothers volcano

Geology ◽  
2019 ◽  
Vol 47 (8) ◽  
pp. 762-766 ◽  
Author(s):  
Cornel E.J. de Ronde ◽  
Susan E. Humphris ◽  
Tobias W. Höfig ◽  
Agnes G. Reyes ◽  
Keyword(s):  
Hydrothermal Fluid ◽  
Porphyry Copper ◽  
Critical Role ◽  
Massive Sulfide ◽  
Wall Rock ◽  
Hydrothermal Activity ◽  
Gold Deposits ◽  
Hydrothermal Systems ◽  
Magmatic Fluid ◽  
Caldera Collapse

Abstract Hydrothermal systems hosted by submarine arc volcanoes commonly include a large component of magmatic fluid. The high Cu-Au contents and strongly acidic fluids in these systems are similar to those that formed in the shallow parts of some porphyry copper and epithermal gold deposits mined today on land. Two main types of hydrothermal systems occur along the submarine portion of the Kermadec arc (offshore New Zealand): magmatically influenced and seawater-dominated systems. Brothers volcano hosts both types. Here, we report results from a series of drill holes cored by the International Ocean Discovery Program into these two types of hydrothermal systems. We show that the extent of hydrothermal alteration of the host dacitic volcaniclastics and lavas reflects primary lithological porosity and contrasting spatial and temporal contributions of magmatic fluid, hydrothermal fluid, and seawater. We present a two-step model that links the changes in hydrothermal fluid regime to the evolution of the volcano caldera. Initial hydrothermal activity, prior to caldera formation, was dominated by magmatic gases and hypersaline brines. The former mixed with seawater as they ascended toward the seafloor, and the latter remained sequestered in the subsurface. Following caldera collapse, seawater infiltrated the volcano through fault-controlled permeability, interacted with wall rock and the segregated brines, and transported associated metals toward the seafloor and formed Cu-Zn-Au–rich chimneys on the caldera walls and rim, a process continuing to the present day. This two-step process may be common in submarine arc caldera volcanoes that host volcanogenic massive sulfide deposits, and it is particularly efficient at focusing mineralization at, or near, the seafloor.

Mineral Deposits of Myanmar (Burma)

10.5382/gb.62 ◽  
2021 ◽  
Author(s):  
Laurence Robb ◽  
Andrew Mitchell
Keyword(s):  
Massive Sulfide ◽  
Gold Deposits ◽  
Late Triassic ◽  
Mineral Deposits ◽  
Magmatic Arc ◽  
Silver Deposits ◽  
Copper Gold ◽  
Lead Zinc ◽  
Lead Nickel ◽  
Complex Geology

Myanmar is richly endowed in natural resources that include tin, tungsten, copper, gold, zinc, lead, nickel, and silver, as well as gemstones. The material covered over a nine-day field trip explores the country’s complex geology, which reflects a collisional history stretching from the Late Triassic to at least Miocene, sited at the eastern end of the India-Asia suture. The country can be divided into three principal metallotects: the Wuntho-Popa magmatic arc, with granites and associated porphyry-type and epithermal Cu-Au mineralization; the Slate Belt (also called the Mogok-Mandalay-Mergui Belt), with multiple precollisional I-type and postcollisional S-type crustal melt granites that host significant tin-tungsten mineralization, and which also are host to a number of orogenic gold deposits; and the Shan Plateau with massive sulfide-type and also MVT-style lead-zinc-silver deposits.

Facies architecture and time stratigraphic relationships of a confined trunk-tributary valley fill and unconfined fluvial system in the backwater of the Turonian Ferron-Notom Delta, Utah, U.S.A.

2021 ◽  
Vol 91 (1) ◽  
pp. 66-91
Author(s):  
David Kynaston ◽  
Janok P. Bhattacharya ◽  
Brad S. Singer ◽  
Brian R. Jicha
Keyword(s):  
Milankovitch Cycles ◽  
Bay Of Fundy ◽  
Northern Australia ◽  
Fluvial System ◽  
Valley Fill ◽  
Gps Survey ◽  
3D Photogrammetry ◽  
Entire Sequence ◽  
Lateral Extent ◽  
Floodplain Deposits

ABSTRACT This paper documents a tidally incised, mudstone-prone tributary valley fill linked to a trunk valley in the backwater limit of the Turonian Notom Delta of the Ferron Sandstone Member, Utah. High-resolution 3D photogrammetry models were used to correlate a 20-m-deep valley between 32 measured sections over a 1 km2 area. A GPS survey and GIS geostatistical tools were used to restore the morphology of the tributary valley. The restored valley floor is interpreted as a surface of tidal erosion, based on the overlying facies and surface morphology. Morphological similarities exist between this tributary valley and modern analogs observed in northern Australia, the Memramcook tributary in the Bay of Fundy, and Pleistocene sediments in the Gulf of Thailand. 40Ar/39Ar dating of sanidine crystals using multi-collector mass spectrometry allow for a re-evaluation of depositional rates and timing of 32 fluvial aggradation cycles (FACs) and 9 fluvial-aggradation cycle sets (FAC sets) in this sequence. The new dates show that the entire sequence was deposited in 15 ± 5 kyr, and show that Milankovitch cycles cannot account for the internal complexity of this fluvial stratigraphy, indicating likely autogenic control of the FAC sets. The lateral extent of FACs in floodplain deposits mapped in outcrop are correlated over tens to hundreds of meters, and scale to estimated channel widths reflecting the autogenic control. FAC sets can be correlated for up to 10 km along depositional strike, which suggest controls unrelated to the dynamics of individual channels and may show some elements of allogenic climate-driven processes.

THE NEW ROYAL OIL FIELD: A CASE HISTORY OF THE DISCOVERY AND APPRAISAL OF A SUBTLE, STRATIGRAPHICALLY TRAPPED HYDROCARBON ACCUMULATION IN THE TRIASSIC SHOWGROUNDS SANDSTONE, SURAT BASIN

2003 ◽  
Vol 43 (1) ◽  
pp. 415
Author(s):  
R.J. Willink ◽  
R.L. Harvey
Keyword(s):  
Case History ◽  
Oil Field ◽  
Reservoir Properties ◽  
Incised Valley ◽  
Valley Fill ◽  
History Of ◽  
Lateral Extent ◽  
Original Oil In Place ◽  
3D Seismic Data ◽  
Field Area

The New Royal Oil Field is located in a structural embayment on the eastern flank of the Kincora High, western Surat Basin, Queensland. Hydrocarbons have accumulated in the Middle Triassic Showgrounds Sandstone, specifically in a thin basal fluvial unit, interpreted as part of an incised valley fill deposit, that displays excellent reservoir properties but is highly localised in its distribution. The Showgrounds Sandstone overlies either granitic basement or a veneer of Permian clastics including coals. Whereas the Showgrounds Sandstone is an established hydrocarbon bearing reservoir in a number of structural settings elsewhere in the basin, trapping in the New Royal field is primarily stratigraphic.Since its discovery in November 1995, various exploration techniques and technologies have been applied, including the acquisition of 3D seismic data, in an attempt to understand the trapping mechanism of this field and predict its lateral extent, albeit with mixed success. Twelve wells have now been drilled in the greater New Royal field area, only four of which were successfully completed as oil producers from the basal Showgrounds Sandstone. Production to date totals 1.1 million barrels of oil and reservoir simulation studies indicate that original-oil-in-place was 4.6 million barrels.This case history serves as a timely reminder that despite all the technology now available to the petroleum geoscientist, serendipity still plays an important role in the discovery and successful appraisal of certain hydrocarbon accumulations in the Surat Basin.

Atmospheric Winds

1950 ◽  
Vol 54 (477) ◽  
pp. 602-605 ◽  
Author(s):  
D. M. Davies
Keyword(s):  
Route Planning ◽  
Jet Stream ◽  
Rates Of Change ◽  
Potential Source ◽  
Lateral Extent ◽  
High Winds ◽  
Very High

The role of meteorology in air operations is becoming increasingly important and an understanding of meteorology is desirable in the consideration of a number of the problems to be faced. The forecasting of winds en route and the use of these forecasts is one such problem, which has been brought into greater prominence by the advent of fast, high-flying aircraft. A great deal of work is being done on upper air winds and it is already clear that curious and significant phenomena sometimes occur. Thus very high winds are sometimes found in belts of limited lateral extent—the so-called “jet stream.” Not only high winds, but high rates of change of wind occur in such regions and they are clearly a potential source of difficulty to the navigator. Apart from the jet stream —a meteorological highlight of recent development—airline operators are also concerned with the problem of route planning.

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