Geology topics
Thomas P Thayer
Publications and source records attributed to Thomas P Thayer.
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.
Preliminary chemical correlation of chromite with the containing rocks
Chromite investigations of the U. S. Geological Survey since 1939 indicate that economic deposits of chromite rich in normative spinel ((Mg, Fe)Al 2 O 4 ) occur in peridotites which are closely associated with gabbro; high-chrome chromites occur in feldspar-free peridotites; and chromites rich in both normative chromite ((Mg, Fe)Cr 2 O 4 ) and magnetite (FeFe 2 O 4 ) are found in the pyroxene-rich stratiform complexes. Reaction of high-alumina chromite with diopsidic gabbro to form anorthite, olivine, and enstatite is described, and some probable equilibria between chromite and silicate minerals are discussed. A plot of 63 complete analyses on a triangular prism of composition shows that chromites from different geologic provinces in the Western Hemisphere vary consistently and fall in overlapping, but distinct, fields. The chromites of the Caribbean Province, which occur in dunite and troctolite, have the general formula Cr (sub 25-80) Al (sub 15-75) Fe (sub 1-5) (Mg (sub 65-75) ) and average about Cr 50 Al 47 (Mg 70 ). The chromites of the Pacific Coast, which occur in dunite and saxonite, average about Cr 70 Al 24 (Mg 60 ) in the range Cr (sub 60-77) Al (sub 16-35) Fe (sub 3-12) (Mg (sub 45-75) ). The stratiform deposits of the Stillwater and Bushveld complexes occur in harzburgite and bronzitite, and are very much alike, averaging Cr 60 Al 32 (Mg 52 ) and Cr 58 Al 34 (Mg 44 ) respectively. Chromites from gabbroic facies of the Bushveld complex are much richer in normative magnetite, presumably reflecting a higher CaO: Al 2 O 3 ratio in the silicate environment.