| Description |
x,129 leaves, 17 plates : illustrations (some colored), maps, photographs ; 29 cm |
| Summary |
"Petrographic, petrochemical and spectrographic studies were completed on selected Precambrian granitic rock samples from Southeastern Missouri. This investigation contributes to a more detailed knowledge of the Precambrian granitic rocks of this part of the state. Petrographic analysis of forty-four thin sections of granitic rocks from the St. Francois Mountains area revealed six different granite types. These have been named the Fredericktown, Knoblick, Doerun, Graniteville, Klondike and Silvermine granites. These rocks form a large part of a composite batholith. More than one period of granitic intrusion is represented, but differentiation also contributed to the formation of this diversity of the rocks. In the Johannsen classification they are classified as leucogranites, granites, alaskites, kalialaskites, sodaclase granites and adamellites. The Niggli petrochemical classification of twenty- seven chemical analyses of these granites revealed their petrogenetic relationships. The chemical character of the magma out of which they have formed was acidic, salic, relatively alkali rich and lime poor. The Doerun, Graniteville and Klondike granites are in the aplitgranitic, the Fredericktown granites and granite porphyries in the aplitgranitic and engadinitgranitic, the Knoblick granite in the granodioritic, and the Silvermine granite in the yosemititgranitic magma type. All the rocks belong to the calc-alkalic petrographic province. Qualitative spectrochemical analysis of forty-four granite samples revealed the presence of the following minor elements: Mg, Sr, Ba, Ti, Zr, V, Cr, Co, Ni, Cu, Ag, Zn, Sn and Pb. Mg, V, Co, Zn, Sn and Pb were selected as index trace elements. The different granite types were characterized according to the relative amounts of these. The Fredericktown granites and granite porphyries, the Knoblick granite and the Silvermine granite contain more Mg, V, and Co, and less Zn, Sn, and Pb than the other granite types. The Doerun, Graniteville and Klondike granites are also relatively high in V and Co. Zn is not always present, but they have more Sn and Pb than the other granite types. Compared with granites from other localities, the Missouri granites are characterized by a consistency of copper, a relatively frequent occurrence of tin, lead and zinc, and a rareness of chromium and silver"--Abstract, leaves ii-iii. |
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