Pegmatites of the Anderson Ridge quadrangle, Fremont County, Wyoming

“The oldest rocks in the area consist mainly of para- schists of low to medium rank and restricted higher rank sillimanite schist. The entire series has been at least double folded. The most apparent are tight north to north- east trending folds. These have been intruded in the northern part of the area by a batholithic body of granitic composition, a granitic stock, a pegmatitic granite, a granitic sill-like body and different types of pegmatite dikes and sills. The youngest intrusions are a series of northeast trending basic dikes and sills. A major easterly trending transverse fault and a series of smaller faults of almost east-west trend are the main fault trends in the area. They are younger than all bodies above. Pegmatites are very abundant and vary in size, shape, texture, and mineralogy. They are more numerous in the north than the south and invade all rock types except the younger basic intrusions. A new classification of the size, shape, and texture of pegmatites is proposed. The size and shape of any individual pegmatite body is identified by two values, namely, the length X width (LXW) value and the length/width (L/W) ratio. Because of the extreme variation in texture of the pegmatite bodies a classification based on a geometric scale is proposed. Both mega- and microscopic sizes applicable to field and laboratory studies are included. Five different mineralogioal types of pegmatites are recognized: magnetite granite, graphic granite, tourmaline granite, garnet granite, and biotite granite. Both concordant and discordant types of pegmatites are present. A few of the concordant varieties show a rough zoned character, but layering is characteristic of the discordant and many of the concordant varieties. The layering may result from textural and/or compositional variations. Coarse and very coarse bands alternate with fine and very fine ones. Also distinct mineralogic variations are common in these different bands. Fine-grained red garnet-rich bands characterize a good percentage of the pegmatites in the area. These colored bands are of great help in determining the internal structure of such bodies. The pegmatites are believed to be of magmatic origin. The temperature of the magmatic fluids, the content of volatiles, and the confining pressure as well as the chemical composition are thought to have varied greatly for the different pegmatite types of the area. Beryl is the most important economic mineral known to date. The very coarse tourmaline granite pegmatites are the most important host for beryl. Coarse perthitic bands and massive quartz bands in the tourmaline garnet granite pegmatites and the garnet granite pegmatites offer some promise as hosts for beryllium minerals. The district is now under active exploration”—Abstract, pages iii-iv

The technique of lineaments and linears analysis and its application in the Minerogenic Province of Southeast Missouri

Current terminology in the field of lineaments and linears (lineations) analysis was reviewed and quantitative definitions of the common terms offered. A general classification of lineations is herein proposed. Characteristics of drainage and airphoto lineations were reviewed and the procedure used in their analysis discussed. An area about 1880 square miles was analyzed for lineations based on drainage networks and the resulting patterns showed preferred orientation. These drainage lineations were later compared with the airphoto lineations of the same area and a limited degree of similarity was observed. The airphoto lineations of an area approximately 7000 sq. mi. covering the Minerogenic Province of southeast Missouri were analyzed using airphoto indexes compiled to a scale of 1 inch:1 mile. To check the consistency of the resulting lineation pattern an area in and adjacent to the Province was similarly studied, based on a high altitude airphoto index sheet. A regional pattern of airphoto lineations was recognized as well as several local interferences. The regional pattern is characterized by a prominent diagonal system and a less significant axial system. The diagonal system includes a northeasterly and a northwesterly set and the axial system a northerly and an easterly set. The diagonal sets are distinct over all the area but the axial system is recognized locally and frequently only one set (the northerly trending) is present. Significant causes of and variables affecting the local patterns are believed to be: local structural disturbances, primary and diagenetic structures in the Paleozoic sediments, buried knobs and ridges, and collapse structures and sink holes. The maximum density of lineation is found in the Precambrian St. Francois Mountains, and the value drops gradually in all directions outside of this area. Major fault trends coincide with major lineation trends in most cases. Repeating lineation pattern in areas of sub-continental to continental scale (Sondar\u27s regmatic shear pattern ) is advocated by many writers. Four major trends, similar to those of he regional pattern of southeast Missouri, are commonly recognized,.The writer reviewed current theories of their origin and concludes that the major fracture pattern of the earth is caused by extra-terrestial forces, such as oscillatory earth tides, and intra-terrestial (tectonic) forces. Internal forces explain the local intensification of the pattern (along all or some of its trends) in some geologic environments. The following conclusions are reached regarding lead deposits in the Minerogenic Province: 1) the lead mineralization was of an epigenetic-hypogene origin, 2) channelways for mineralization followed one or more directions of the four regional lineations of the Precambrian complex. These trends also affected the shape of the basins of sedimentation, and the trends of the linear primary and diagenetic features of the sediments, 3) the lead deposits are controlled by: a) the primary and diagenetic linear structural features which reflect the lineation pattern of the basement, b) buried Precambrian knobs (with their local fracture patterns), and c) the regional fracture pattern of the sediments which is essentially similar to that of the Precambrian basement, and 4) ore shoots and extensions of known ores are likely to be aligned parallel to one or more of the four regional lineation sets. This condition applied also for the Precambrian iron ores and the rich runs of the residual barite deposits in the Province --Abstract, pages i-ii