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Eric R. Force

Publications and source records attributed to Eric R. Force.

13 recordsLinked to original sources
USGS2007

Type region of the Ione Formation (Eocene), central California: Stratigraphy, paleogeography, and relation to auriferous gravels

The middle Eocene Ione Formation extends over 200 miles (320 km) along the western edge of the Sierra Nevada. Our study was concentrated in the type region, 30 miles (48 km) along strike. There a bedrock ridge forms the seaward western side of the Ione depositional tract, defining a subbasin margin. The eastern limit of the type Ione is locally defined by high-angle faults. Ione sediments were spread over Upper Mesozoic metamorphic and plutonic bedrock, fed by gold-bearing streams dissecting the western slope of the ancestral Sierra Nevada. By middle Eocene time, a tropical or subtropical climate prevailed, leading to deep chemical weathering (including laterization) and a distinctively mature mineral assemblage was fed to and generated within Ione deposits. The Ione is noted for its abundant kaolinitic clay, some of it coarsely crystalline; the clay is present as both detrital grains and authigenic cement. Quartz is abundant, mostly as angular grains. Heavy mineral fractions are dominated by altered ilmenite and zircon. Distribution of feldspar is irregular, both stratigraphically and areally. Non-marine facies are most voluminous, and include conglomerates, especially at the base and along the eastern margins of the formation where they pass into Sierran auriferous gravels. Clays, grading into lignites, and gritty sands are also common facies. Both braided and meandering fluvial facies have been recognized. Shallow marine waters flooded the basin probably twice. Tongues of sediment exhibiting a variety of estuarine to marine indicators are underlain and overlain by fluvial deposits. Marine body fossils are found at only a few localities, but burrows identified as Ophiomorpha and cf. Thalassinoides are abundant in many places. Other clues to marginal marine deposition are the occurrence of glauconite in one bed, typical relations of lagoonal to beach (locally heavy-mineral-rich) lithofacies, closed-basin three-dimensional morphology of basinal facies, and high sulfur content of some marginal coals. The Ione has been said to be deltaic; however the two transgressional-regressional cycles we propose imply that only the regressional parts were deltaic. At other times, much of the type Ione would better be termed an intertidal estuary. Because the lower marine sequence was deposited against a paleobasin margin on the west, deltaic morphology was constrained, but apparently progradation was from north to south despite drainage into the basin from the east. Relations to the south are unclear due to the Stockton arch. The eastern margin of the type-Ione basin, and to some extent even its marine facies, are poorly constrained. A surface on Sierran bedrock to the east may have been stripped of some Ione basinal facies, leaving only coeval entrenched fluvial channel deposits.

California↗
USGS2006

A Lower Carboniferous two-stage extensional basin along the Avalon-Meguma terrane boundary: Evidence from southeastern Isle Madame, Nova Scotia

Anomalously thick and coarse clastic sedimentary successions, including over 5000 m of conglomerate, are exposed on Isle Madame off the southern coast of Cape Breton island. Two steeply to moderately dipping stratigraphic packages are recognized: one involving Horton and lower Windsor groups (Tournasian–Visean); the other involving upper Windsor and Mabou (Visean–Namurian) groups. Also anomalous on isle Madame are three long narrow belts of “basement” rocks, together with voluminous chloritic microbreccia and minor semi-ductile mylonite, which are separated from the conglomerate-dominated successions by faults. The angular relations between the cataclastic rocks and the conglomerate units, combined with the presence of cataclasite clasts in the conglomerate units and evidence of dip-slip faults within the basin, suggest an extensional setting, where listric normal faults outline detachment allochthons. Allochthon geometry requires two stages of extension, the older stage completed in early Windsor Group time and including most of the island, and the more local younger stage completed in Mabou Group time. Domino-style upper-plate faulting in the younger stage locally repeated the older detachment relation of basement and conglomerate to form the observed narrow belts. Re-rotation of older successions in the younger stage also locally overturned the Horton Group. These features developed within a broad zone of Carboniferous dextral transcurrent faulting between already-docked Avalon and Meguma terranes. Sites of transpression and transtension alternated along the Cobequid-Chedabucto fault zone that separated these terranes. The earlier extensional features in isle Madame likely represent the northern headwall and associated clastic debris of a pull-apart or other type of transtensional basin developed along part of this fault zone that had become listric; they were repeated and exposed by being up-ended in the second stage of extension, also on listric faults. The two-stage history on isle Madame exposes the deeper parts of one of the Horton-age extensional basins of the Maritimes, others of which have been described as half-grabens based on their shallower exposures.

Nova Scotia↗
USGS2006

The Ajo Mining District, Pima County, Arizona: Evidence for middle Cenozoic detachment faulting, plutonism, volcanism, and hydrothermal alteration

Introduction: The Ajo porphyry copper deposit and surrounding Upper Cretaceous rocks have been separated from their plutonic source and rotated by detachment faulting. Overlying middle Cenozoic sedimentary and volcanic rocks have been tilted and show evidence for two periods of rotation. Following these rotations, a granitic stock (23.7?0.2 Ma) intruded basement rocks west of the Ajo deposit. This stock was uplifted 2.5 km to expose deep-seated Na-Ca alteration.

Arizona↗
USGS2001

Eagle Mountain Mine: Geology of the former Kaiser Steel Operation in Riverside County, California

This investigation of the Eagle Mountain Mine area, though cursory, revealed new structural, alteration, and stratigraphic relations. Eagle Mountain ores were previously an important source of iron to the western U. S. Ore (where fresh) is magnetite-pyrite rock forming two stratabound horizons virtually continuous for 11 km. Gneissic basement rocks are overlain by two sedimentary units, separated by unconformities. The lower unit contains carbonate rocks and quartzite; the "vitreous quartzite" of previous workers, however, is an alteration feature rather than a stratigraphic one. The upper unit contains thick conglomerates. This layered sequence of rocks is deformed into a west-plunging anticline. Intrusion by Jurassic quartz monzonite apparently followed this deformation. Quartz monzonite forms a branching network of sills, some of which dilate the contact between the upper and lower sedimentary sequences. Intrusion resulted in extensive, mostly-anhydrous skarns, but stratabound iron ore is just as closely related to some other features: regional alteration of quartz monzonite, with iron ore adjacent to little-altered rocks along the boundary between sodic and potassic domains, the two unconformities, which apparently formed stratigraphic traps for precipitation of stratabound iron ores, a north-facing monoclinal plane between folds, which was preferentially replaced. Iron ore replaces a variety of host rocks along the two unconformities, forming massive to globular bodies, and its mineralogy correlates with deuteric alteration features, not anhydrous skarn. Its pyrite contains as much as 3% cobalt. Iron was only one of five elements that showed mobility in this region on a scale that suggests basic crustal processes. The others in probable order of flux magnitude are silica, magnesium, sodium, and potassium, to form regionally distributed “vitreous quartzite”, dolomite, and secondary feldspars, respectively.

California↗
USGS2000

Titanium mineral resources of the western U.S.: An update

Thirteen deposits or districts in the western U.S. have been examined in which titanium mineral resources have been reported or implied. These deposits are of the following general types (in probable order of importance): 1) Cretaceous shoreline placer deposits, 2) silica-sand deposits of California, 3) fluvial monazite placers of Idaho, 4) anorthosite related deposits, and 5) clay and bauxite deposits of the northwestern U.S. Relative to previous reports, this one shows some greater and some lesser resources (table 1). In any case, titanium-mineral resources of the western U.S. (west of 103° longitude) remain modest at world scale except as unconventional (especially perovskite) and by-product (especially porphyry) resources. Some deposits, however, have enhanced value to the titanium explorationist for the geologic relations they illustrate. Among the new conclusions are: a) Loci of Cretaceous shoreline placers form linear patterns, nested as a function of age, that can be traced for thousands of kilometers, permitting focused exploration in whole new mountain ranges. b) Medial hematite-ilmenite solid-solution, which is highly magnetic, is a major carrier of TiO 2 values in the Cretaceous deposits of Wyoming. This phase was previously thought to be relatively rare. c) Regressive shoreline placer deposits in indurated Cretaceous sequences expose intricate facies relations, such as the construction of shoreface sequences by long-shore drift over tidal-channel fill, without much loss of paleogeographic information. d) Due to deep weathering, virtually every Eocene sediment that accumulated in the Ione basin at the foot of the Sierra Nevada has economic value, permitting recovery of altered ilmenite and zircon along with silica, clay, coal, and gold. Ilmenite is most abundant in newly recognized shoreline sands. e) Upper Tertiary fluvial placers of Idaho formed in and filled fault-bounded basins and thus are far more voluminous than deposits in the modern valley system. Previously reported resources are thus far too low. f) Mafic igneous rocks of Proterozoic age near Bagdad, Arizona are of ophiolitic affinity, but contain nelsonitic ilmenite enrichments associated with anorthositic layers.

Open-File Report↗
USGS1978

Uranium and phosphate resources in the Cooper Formation of the Charleston region, South Carolina

Phosphate deposits formerly exploited in the Charleston district were formed by weathering and reworking of the Cooper Formation (Eocene and Oliogcene). Previous workers have shown that unusual concentrations of uranium occur in phosphate-rich nodular material formed during subareal weathering. We found that the old mining district is on an erosional high of the Cooper Formation and in a topographic depression, but that the process of weathering enrichment of the Cooper Formation extends beyond the mining district. Fresh sediments from the Cooper Formation average 14.5 ppm uranium and 1.0 percent P 2 0 5 for Oliogcene samples and 5.6 ppm U and 0.15 percent P 2 0 5 for Eocene samples. Zones of secondary enrichment over undifferentiated Cooper Formation average 2 m thick and have average values of 60 ppm U and 5.4 percent P 2 0 5 . No deposits clearly of economic importance were found, although detailed studies may reveal such deposits.

South Carolina↗
USGS1974

Geology of the Sanokole Quadrangle, Liberia

As part of a program undertaken cooperatively by the Liberian Geological Survey (LGS) and the U. S. Geological Survey (USGS), under the sponsorship of the Government of Liberia and the Agency for Inter-national Development, U. S. Department of State, Liberia was mapped by geologic and geophysical methods during the period 1965 to 1972. The resulting geologic and geophysical maps are published in ten folios, each covering one quadrangle (see index map). Systematic map synthesis by Force began in 1971 and included field data as shown on figure 1. Observations but not interpretations made by Offerberg and Tremaine (1961) were incorporated in the mapping. The area compiled by Berge (fig. 1) is the LAMCO (Liberian American-Swedish Minerals Co.) Nimba Concession Area. Mapping has been done by company geologists since 1955 and summarized by Berge (1966, 1968, 1973, 1974). Detailed mapping has been done in many areas underlain by iron deposits, but the concession area as a whole has been mapped only by reconnaissance methods. For both compilers, photogeologic mapping and the interpretation of air-borne magnetic and radiometric surveys (Behrendt and Wotorson, 1974, a and b) are integral to the interpretation as shown.

Open-File Report↗
USGS1974

Geology of the Zwedru Quadrangle, Liberia

As part of a program undertaken cooperatively by the Liberian Geological Survey (LGS) and the U. S. Geological Survey (USGS), under the sponsorship of the Government of Liberia and the Agency for International Development, U. S. Department of State, Liberia was mapped by geologic and geophysical methods during the period 1965 to 1972.

Zwedru Quadrangle↗