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Show l ' li ' There Are Many Geological Rea- Hj, jjj S011S Depth Musi J3e Hjf J MANY MINES HAVE BEEN OVERLOOKED Mi p ; Extension of the Mineralized . tl Area Would Have Very Im- ; A portant Effect. ;4 I t Any noiablo extension of the produc- k J luff area of Goldfield, Nov., would be , welcomed, not only iu the district, but. "'; jj throughout the country, as a mutter 1,1 ' j of much commercial importance. The T. ' gold output of that small acreage cov- H- ered by tho Goldfield Consolidated and U1; j Florence properties has, during the past HhI I three years, been so extraordinary for BJH j ' a now district, that the attention of Bk j ' 't Investors and operators has beou very Hf I closely centered upon it, and to the Hl j' neglect of a belt lying east of tho BF J Rod Top, Mohawk, and Jumbo mines H'ft j thai seems worthy of more serious de- Hf: f' velopment than has yet been attempt- Hll; 1 1 cd, says tho Mining and Scientific Hs. 'Press. The region in question differs from H.i; jt that of the proved belt by reason of a ' fault, noted by Ransome in his mono- t ' graph on tho geology- of Goldlleld; this B - fault strikes roughly north-south and i to the west of the St. Ives and Velvet HV , ' properties. "West of this fault, and cs kj , rending to the Columbia Mountain BL, i fault, is an area of dacitc wliich has ft, 1 1 Hot been bottomed at 600 feet, tho f j i i deepest workings in the Mohawk mine Kl ' and in the district. East of tlie fault f?' nnd extending to the granito of Vindi- Hf calor mountain, is an extensive area, Tf. K, over part of which dacite appears at H'rf ' the surface. This daciio is of shallow l ( depth from 100 to 200 feet and is underlain by a sheet of the early nude- F - site, of the region. This, in turn, at ! 1 depths varying, as far as observed, J from 200 to 350 feet, is underlain by I- , a second sheet of dacite. Tho impor-ti impor-ti tance of this fact, from a geological '! viewpoint, is great. The commercial ( possibilities can be appreciated only by those who know the relative value I ( of dao.ito among the country rocks of , the Goldfield district. Of the rocks j named only three need be here con-' con-' i sidered: Tho earlier andesite, whiiish-, whiiish-, ffrarf containing much liornblende and 'P, thereby readily distinguished, which is the prevailing countiy rock west of the Columbia mountain fault, and in which I ' no payable veins have so far been found at Goldfield, iu spito of much de-' de-' j velopment; the later andesite, dark JTray, withjhonocrysls of feldspar and with a fairly smooth clca-vage; and dacite, similar chemically to the later if andesite but distinguished by a rough ij cleavage, the presence of "occasional . cuariz phonoerysts, aud a lighter color H when weatliered. Tho first of theso ' rocks hus apparently no commercial unit un-it t portance whatever. The second has 8( possibilities, as indicated in tho Daisy J ' mine at Diainoudneld. Tho third, da- cite, is the country rock of tho Mohawk, Red Top, Combination. Jumbo, Jum-bo, and Florence mines. It is suffi-cicntl.y suffi-cicntl.y obvious that operators at Gold-field, Gold-field, having before tiicm tho remarkable remark-able yield of thoso mines, should seek to develop veins occurring in tho same country rock and close by. That this has not been done more vigorously is doubtless due to lack of understanding of the geology of that part of the district. dis-trict. In the belt with which this article particularly deals, several properties have yielded pay ore, some of it rich, from veins that continue downward strongly as far as developed but al-wa3-s, with ono exception, from near the surface. Among these properties are .the St. Ives, "Velvet, Blue Bell, Blue Bull, North Star and Cimmaron. Always Al-ways the ore ceased, or nearly so, as tho underlying andesite was approached. ap-proached. Tho exception is tho St. Ives, where both the mine and lease shafts have pcutrated the lower dacite, wherein, I am creditably informed, hiirh-grade ore has again been found. This is tho sole evidence, so fnr, that this lower dacite- sheet is of tho same character as that of tho Mohawk-Flor-cuco belt; but it would seem sufficiently good evidence to eucourago owners of neighboring claims covering strong veins to develop deeper into country that is favorable. Heretofore, operations opera-tions havo generally ceased as surface ore failed. In some cases, large sums have been spent in developing veins within the andesite sheet at depths of from 1 200 to 300 feet with entirely negative results. A liko expenditure at a depth of 500 feet might possibly have developed good mines. The dacite ot the Goldfield district is later than tho first andesite and appears ap-pears as intrusive sheets, lying rather flat and presumably following lines of weakness. Ransomo notes a single such sheet, which appears at the surface, and the underlying first andesite. Tho lower dacite sheet does not come to the surfaco auj'where, but is shown in several sev-eral shafts, the most westerly of these being the St. Ives and the most easterly the Old Kenluck. near Viudicator mountain. How thick this lower sheet may be there is as yet no evidence; but that it is of the same origin as tho upper sheet, thrown off from the same moro or less vortical iustrusion, I can 6ec no goofl reason to doubt. It follows, fol-lows, logically, that there may be several sev-eral such sheets separated by tho older country rock. It- also follows that if Iiansome's north-south fault is normal, as it probably is, tho first andesite of tho St. Ives will be found to underlie the dacite of the Mohawk and Florence Flor-ence mines at a depth yet to be determined. deter-mined. In such event there will be consolation in the fact that a lower sheet of dacite is known to exist and that all tho evidence shows the veins to continue, uninterruptedly through theso variations of country rock. |