Bisbee daily review., 1916-04-16

evaporation. The winters are mild and the summers, while hot during the day have yet fairly cool nights. The vegetation consists of cacti, greasewood. yuccas and sagebrush, and does not interfere in any way with prospecting. Prospecting is made easy by the baroness of the rocks, except where they are covered by re- cent surface wash.
 Geology of the District.
 The country belongs to the geologic province of the Basin ranges of which it forms the southern part, and which is so characteristic of many mining districts of Nevada.
 Oatman is located on the western slope of the Black range, which com prises an important range of noun tains about 10 miles in width, run ming north and south between Sacra- mento valley, where Kingman is sit uated, to the east and the Mohave val ley through which flows the Cobra do river to the west.
 Geologically, the range is formed by | the pre-Cambrian granitoid complev, flanked, overlain and in the south ern part deeply buried by extensive areas of Tertiary volcanics.
 The volcanic rocks consist mainly of an older andesite, supporting a green chloritic andesite, in which many of the main ore bodies are form ed, overlain by a series of flows of trachytic, rhyolitic and andesitic la vas, tuffs and breccias, and capped in many places by basaltic flow. The Tom Reed-Gold Road district is characterized by two sets of veins and dikes running at a more or less acute angle to each other. One set of veins run N. 10 degrees w. like the Pasa- dena vein to N. 50 degrees w. like the Tom Reed and Gold Road veins. The other set runs almost east and west, or N. 75 degrees to 0 degrees w. like the Times, the Hardy and the Gaddis and Perry veins.
 The Veins of the District.
 The veins are really large lodes made of sheeted fracture zones, very persistent for lengths of several miles. In many cases they form some out crops very prominent in the land scape.
 The prominence of the vein outcrops q country rock in which they occur. In the trachytes or rhyolites. what Schra der has called the Undifferentiated Tertiary volcanics. or in the microgra mite they are quite conspicuous On the contrary, when the lodes outcrop in the green chloritic andesite they are inconspicuous and difficult to trace in an astonishing degree. I am in clined to think that the cross lodes of the nearly east and west system have had a very important genetic influ ence in the location and the emplace- ment of the ore bodies in the lodes of the nearly north and south sys- tenn, such as in the Tom Reed, Gold Road, United Eastern and Big Jim mines, for instance. Faulting and hori zontal displacement along the vein. without much downward throw is no ticeable. Some engineers give it as the reason of the lenticular shops of some important ore shoots, like the one opened up in the United Eastern mine. 1 did not see any clear evi dence to support that theory there, and l think that it can be well ques- toned whether or not such is the case.
 The Ore Deposition.
 l believe also that the special fea ture of the district, namely, the fact that several of the most important ore bodies do not come to the surface, is the consequence of the chemical com position of the ascending hot waters which have formed them. The veins contain a large percentage of calcite mixed with the quartz. This feature is connected with the lack of metas omatic replacement which is quite characteristic of the ore deposits of the district It is remarkable to see in the best ore of the United Easteern, Big Jim or Gold Road mines, pieces of andesite or other country rock surrounded by quartz or calcite, and not altered at all. In the veins of the Cripple Creek or Goldfield districts, such pieces would have been com pletely altered But in the Oatman district this is not the case. think that the hot ascending waters were already saturated with lime. When deposited their gold they were unable to dissolve and to silicify the feldspars and the ferromagnesian minerals of the country rock between the Assures, even microscopic in size, of the shear ed zone forming the lode. While they were depositing the gold values, in all these small cracks at the same time they left the wall rock of these cracks almost unaltered. Later the large amount of calcite in all the fractures was much more easily dissolved and carried to a lower level by the sur face waters in their downward mlgra- tion, without leaving as much traces behind as would have been the case if this phase of vein transformation had reacted on a strong vein formed esz11so A