Total-count gamma radiation map of the Zorzor quadrangle, Liberia
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Open-File Report↗
Geology topics
Research about Liberia
Source-linked reports with geographic coverage including Liberia.
Aeromagnetic and gravity investigations of the Coastal Area and Continental Shelf of Liberia, West Africa, and their relation to continental drift
An aeromagnetic survey has shown the existence of several basins in which magnetic basement depths are greater than 5 km on the continental shelf off Liberia. Magnetic diabase of 176 to 192 m.y. (Jurassic) in age intruding the Paleozoic (?) rocks and overlain by younger rocks onshore requires the distinction between “magnetic basement” and “basement.” Several lines of evidence suggest that the Paleozoic(?) rocks are less than 1 km thick; this implies that the diabase does not introduce a large error in depth-to-basement estimates. The dikes or their extrusive equivalents are traceable, on the basis of the magnetic data, beneath the younger sedimentary rock in the basins to the edge of the continental slope. The magnetic data also delineate a second zone of diabase dikes 90 km inland, parallel to the coast, which cross the entire country. The intrusion of the younger dikes probably coincides with rifting at the beginning of the separation of Africa and South America, and the associated magnetic anomaly zones appear to be parallel with and continuous into the anomaly bands in the Atlantic. A major northeast-trending break in the magnetic fabric intersects the coast near 9° W. and is associated with Eburnean age rocks (about 2000 m.y.) to the southeast as contrasted with Liberian-age rocks (about 2700 m.y.) to the northwest. Change in magnetic fabric direction inland from northeast to northwest in the coastal area allows recognition of a boundary between the Liberian-age rocks inland and Pan-African-age (about 550 m.y.) rocks in the coastal area northwest of about 9° 20'W. Sets of north-northwest-and west-northwest—trending faults of 1 to 2 km vertical displacement cut the Cretaceous sedimentary rocks onshore and can be traced into the offshore basins. Vertical displacements of several kilometers in the magnetic basement underlying the continental shelf suggest a pattern of block faulting all along the coast and continental shelf. Negative Bouguer anomalies exist over two Cretaceous basins in the coastal area; a negative Bouguer anomaly exists over one of the basins southwest of Monrovia, as shown by a marine traverse, suggesting that Cretaceous or younger sedimentary rocks fill these basins also. A 50 to 60 mgal positive Bouguer anomaly area exists along the coast from Sierra Leone to Ivory Coast. This anomaly correlates with mafic granulites in the Monrovia region, where the gradient is too steep to be entirely due to crustal thickening at the continental margin and may be related to tectonic activity associated with the basins. The only major break in this positive anomaly above basement rocks along the entire coast of Liberia is over granite gneiss adjacent to (and presumably underlying) the only onshore basins on the Liberian coast. Three seismic reflection profiles support the interpretation of a substantial section of sedimentary rock offshore. A suggested sequence of events indicates tectonic activity in the periods about 2700, about 2000, and about 550 m.y. B.P.; uplift and exposure of deep crustal rocks; deposition of Paleozoic sediments; intrusion of diabase dikes in inland zones; intrusion of 176 to 192 m.y.-old dikes and sills accompanying separation of Africa and South and North America; block faulting along coast and continental shelf, and active sea-floor spreading; filling of basins in Cretaceous and Tertiary(?) time; basaltic extrusion on spreading sea floor and sedimentation on continental shelf and slope.
West Africa↗
Silica sand deposits in the Monrovia area, Liberia
Thin surficial deposits of white silica sand occupy much of the flat coastal area of Liberia from Monrovia to Buchanan 100 km southeast; most of the sand is of good quality for glass manufacture. A lagoonal mode of origin is suggested for these essentially monomineralic deposits. Based on the average thickness of one meter and a conservative bulk density of 1.6, the easily accessible deposts along the Freeway, the Kakata highway, and the Schieffelin road cover about 68 square kilometers and contain at least 109 million metric tons of silica sand.
Open-File Report↗
Geology of the Bushrod Island-New Georgia clay deposit near Monrovia, Liberia
The Bushrod Island-New Georgia clay deposit near Monrovia, Liberia, consisted of interlensing clay and very fine to fine quartz sand; it was deposited in elongate subparallel troughs that had been eroded in coarse-grained sediments. The troughs are interpreted as abandoned stream channels on a former delta of the St. Paul River. The clay of the deposit is essentially a quartz-rich kaolinitic clay that has undergone sufficient weathering in the upper part of the deposit to redistribute iron and alumina. The clay may be divided into three groups: an iron-rich group (A) in which total iron expressed as Fe 2 O 3 averages 6.5 percent and ranges from 4.4 to 9.2 percent, a group (B) relatively lower in iron in which total iron expressed as Fe 2 O 3 averages 2.7 percent and ranges from 1.6 to 7.4 percent, and a group (C) high in both organic material and iron in which total iron expressed as Fe 2 O 3 averages 3.9 percent and ranges from 3.3 to 4.9 percent. Potential indicated reserves for the three groups are estimated at 1,800,000, 5,300,000, and 470,000 tons, respectively. Tests of the physical properties of the raw and fired clay indicate the clay is suitable for the following commercial uses: building brick, hollow tile, drain tile, roofing tile, quarry tile, flower pots, porous earthenware, low to intermediate duty refractory products, and probably stoneware and small diameter sewer pipe.
Monrovia↗
Geologic reconnaissance in western Liberia
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Special Publication↗
Feasibility study for an airborne geophysical survey of the Republic of Liberia
A feasibility study for an airborne geophysical survey of the Republic of Liberia indicates that airborne magnetometer and airborne scintillation detector surveys would be useful 1) in providing support for the current geologic mapping program, 2) as a guide in locating concentrations of economic minerals, and 3) delimiting the extent of known mineral deposits. Preliminary study of earlier airborne magnetometer surveys covering several iron ore localities shows that future geophysical surveys should be flown at a slightly closer flight-line spacing, and that the iron ore localities are characterized by anomalies interpreted as being produced by rocks having a strong anomalous remanent magnetization. In areas of the United States and Canada underlain by crystalline rock types similar to those found in Liberia, airborne geophysical surveys have been successful in locating additional buried economic mineral deposits, in extending known economic mineral deposits, and in contributing useful information to geologic mapping programs, especially in areas overlain by thick glacial deposits or by weathered rock. Some problems regarding the availability of accurate base maps for Liberia, combined with the inherent complex relationships that exist between a rock's geological properties and its magnetization, are briefly reviewed. The importance of obtaining a meaningful geologic interpretation of the geophysical data and coordinating the geophysical survey with the geological mapping program is stressed. Specifications and tolerances for the proposed airborne magnetometer and scintillometer survey of the Republic of Liberia are outlined.
Open-File Report↗
The Mt. Montro kyanite deposit, Grand Bassa County, Liberia
The Mt. Montro kyanite deposit, 14 miles north of Buchanan, Grand Bassa County, Liberia, is near the middle of a belt of kyanite-bearing gneisses and schists that is 9 miles long and 1 mile wide. The deposit, which seems to be the most persistent and the largest single body of kyanite rocks in the belt, is approximately 12, 600 feet long, as much as 480 feet in outcrop width, and from 25 to 350 feet thick. Kyanite-quartz-biotite-feldspar-garnet-muscovite gneiss, local interbeds of kyanite-mica schist, and lesser amounts of biotite-quartz gneiss, are the principal rocks in the deposit. Other rocks in the kyanite belt include garnet-biotite gneiss, undifferentiated quartzo-feldspathic gneiss, quartzite, and amphibolite. The rocks are the product of regional metamorphism to almandine amphibolite facies. The regional strike is northwest and dips are southwest. Kyanite crystals are as much as 3 inches long. The kyanite content ranges from 5. 8 to 46. 7 percent, but most rocks contain between 10 and 35 percent. Garnetiferous beds contain as much as 15 percent red garnets that range to half an inch in diameter. In general, the garnet-rich beds are found in the upper part of the deposit. he total reserves of the Mt. Montro kyanite deposit are estimated at about 10 million tons of kyanitic rock containing approximately 2.5 million tons of kyanite. These estimates include measured, indicated, and inferred reserves, calculated to depths of 25 to 100 feet, on the assumption that open-cut mining to those depths would be feasible. The largest part of the deposit underlies Mt. Montro and contains about 8 million tons of kyanitic rock containing nearly 1.9 million tons of kyanite. Residual soil overlying the deposit averages about 5 feet in thickness and is estimated to comprise slightly more than 400,000 cubic yards of material containing about 186,000 tons of kyanite. The proximity of the kyanite deposit to a paved highway, to port facilities at Buchanan, and to water, electrical power, and timber resources are considered favorable factors relevant to possible development.
Grand Bassa County↗
Phosphate mineralization at Bomi hill and Bambuta, Liberia, west Africa
Iron phosphate minerals which cement talus ore below cliffs formed by massive magnetite- hematite deposits at Bomi hill, Liberia, and also occur in place in fissures and caves in the ore both at Bomi hill and Bambuta, were formed by the interaction of bat dung and iron oxides. The minerals include leucophosphite (previously known only from Western Australia), phosphosiderite, and strengite. Analyses of the leucophosphite are included.
West Africa↗
Preliminary report on iron ore reserves at Bomi Hills, Liberia
At the request if the Liberian Government made through the Department of State of the United States Government, a party of geologists of the Geological Survey, United States Department of the Interior, was sent to Liberia to examine certain mineral deposits. The party, consisting of Walter H. Newhouse, Thomas P. Thayer, and Arthur P. Butler, Jr., left Washington, D.C., about December 1, 1943, and arrived in Monrovia, Liberia, December 12, 1943. They left Roberts Field, Liberia, May 5, 1944, and returned to Washington May 16, 1944. The geologists left Monrovia for field work in the interior on January 9, the delay of several weeks being due to difficulties in obtaining porters. Mr. Arthur Sherman, Mining Engineer for the Liberian Government, who accompanied the party into the interior, capably participated in the examination of the iron deposits and otherwise rendered invaluable assistance sue to his extensive knowledge of the native tribes and trails. President Tubman requested that the part first examined the iron deposits at Bomi Hills. At the close of the work there he requested that iron deposits in the Kpandemai Mountains be investigated. The party therefore left Bomi Hills on March 25 and arrived at Jordense Camp in the Kpandemai Mountain region on April 6. Four days were spent at this place examining the iron mineralization in the vicinity of Castle Rock, Sugar Loaf, and Mt. Wutivi of Kpandemai Mountains. On April 11 Kpandemai village reached. One day was spent on a long transverse into the Kpandemai Mountains to investigate the iron mineralization. The party left Kpandemai Village April 15 and arrived at Monrovia April 27. The iron mineralization in the portions of the Kpandemai Mountains investigated by the party is believed to be too low in grade and too small in amount to be of any present commercial interest and will not be considered further in this report.
Bomi Hills↗