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Opaque oxide minerals of some diabase-granophyre associations in Pennsylvania

Davidson, A. and Wyllie, P. J. (1968) Opaque oxide minerals of some diabase-granophyre associations in Pennsylvania. Economic Geology, 63 (8). pp. 950-960. ISSN 0361-0128. doi:10.2113/gsecongeo.63.8.950.

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Optical examination of the opaque oxide minerals in specimens of diabase, intermediate granophyric diabase, granophyre, and diabase pegmatite from Triassic intrusions of Pennsylvania revealed distinct changes through the diabase-granophyre differentiation sequence. Qualitative electron microprobe scans across complex mineral grains supplemented and confirmed the optical interpretations. The opaque oxide minerals consist almost entirely of ilmenite, magnetite, and ulvospinel, and they comprise between 1 and 10 percent of the rocks in the diabase-granophyre sequence. Magnetite occurs in two forms: the first contains exsolved ulvospinel and is intimately associated with ilmenite; the second is Ti-poor and it does not contain microscopically visible Ti-bearing phases. The second form occurs as rims on the first or as separate crystals in differentiated rocks. Ilmenite occurs as intergrowths, as skeletal growths, and as individual crystals. Accompanying the igneous differentiation sequence there is a gradation from titaniferous magnetite with ilmenite, to skeletal ilmenite retaining an original spinel outline. We suggest that during the stage of iron-enrichment in the igneous differentiation sequence an aqueous fluid developed within the crystallizing intermediate magma and was capable of dissolving iron from the titaniferous magnetite intergrowths, leaving skeletal crystals of ilmenite. Some or all of this iron was redeposited as a second generation of Ti-poor magnetite within the source rock. It is possible that iron-bearing solutions so derived could escape to higher levels where they would be a potential source of magnetite deposits of Cornwall type.

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Additional Information:© 1968 Society of Economic Geologists. June 24; October 24, 1968. We wish to thank Drs. A. A. Socolow and D. M. Lapham of the Pennsylvania Geologic Survey for their interest and advice during this project and for critically reviewing an early draft of the manuscript; Dr. Lapham guided and facilitated visits to Cornwall and other localities where samples were collected. Dr. Christopher Crowe, formerly of the Pennsylvania State University, kindly allowed us to make use of diamond-drill core intersecting diabase near Warwick, and granophyre near Heidlersburg, Pennsylvania. The work was supported by grant MCS-5800 from the Mineral Conservation Section, College of Mineral Industries, The Pennsylvania State University, and preparation of the manuscript was facilitated by grant GA-923 from the National Science Foundation. We are grateful to Dr. A. Rose of the Pennsylvania State University and to Dr. T. N. Irvine of the Geological Survey of Canada for their helpful comments and criticisms of the manuscript.
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Pennsylvania State UniversityMCS-5800
Issue or Number:8
Record Number:CaltechAUTHORS:20160129-093649285
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Official Citation:A. Davidson and P. J. Wyllie Opaque oxide minerals of some diabase-granophyre associations in Pennsylvania Economic Geology, December 1968, v. 63, p. 950-960, doi:10.2113/gsecongeo.63.8.950
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64087
Deposited By: Tony Diaz
Deposited On:29 Jan 2016 20:10
Last Modified:10 Nov 2021 23:25

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