Mineral Resources of Michigan with Statistical Tables of Production and Value of Mineral Products for Volume 16 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 Excerpt: ...in these veins. Prehnite is pseudomorphic after plagioclase; and many amygdaloids are largely prehnitized. The prehnite is again replaced by otrhoclase; and finally, the latter may change into epidote and quartz. Sericite is absent. "These copper-bearing veins are clearly very different from the majority of fissure-veins, and have been formed under very different conditions--in fact, probably not by the thermal waters. Of other classes, the orthoclase-albite-zeolite veins of the Alps are most closely related: while a certain slight resemblance also exists to the propylitic veins, emphasized by the chloritic alteration and the presence of orthoclase." Dr. Lindgren in his recently published book on Mineral Deposits discusses the origin of the native copper and of the zeolites which occur with the copper in basic lavas. He points out that of all the occurrences of zeolites the most abundant and conspicuous is that in the blowholes of volcanic flows, and states that in many occurrences it can be shown that the zeolites formed as the last phase of consolidation of a magma. He discredits the frequently made statement that zeolites are formed as the result of leaching by surface waters and says: "Trans. A. t. M. E., 1901. p. 145. tTrans A. I. M. E., Genesis of Ore Deposits, 1901, pp. 606-60H. "Zeolites are manifestly unstable in the zone of weathering and must have been formed at some depth. Of late years the opinion has been gaining ground that zeolitization, in basic volcanic rocks is distinctly connected with the cooling processes and in fact should be regarded as an after effect of volcanism, their deposition taking place in the still hot rocks." He believes, with Knopf, that any theory accounting satisfactorily for the zeolites will a...