Show GEOLOGY OF JOHNNIE DISTRICT LOS ANGELES MINING REVIEW 11 los angeles mining review before the california academy of science on the evening of monday last professor james stirling late government geologist of victoria australia member of the royal institute london and of other leading english and colonial learned societies cie ties delivered a valuable lecture upon the geological structure of the johnnie johnn e district lincoln county nevada professor stirling laid particular stress upon the value of petrography in mine examination and illustrated his point by a number ot of lantern slides of rocks of the district showing particularly the transformation of the and of the carboniferous lime stones sandstones and had been subject to the action of heated solutions forming bluffy outcrops and the lateral spurs by sinuous curves of cherty lime stones the low undulating foothills merge at lower levels levela into the gently sloping surfaces of the tertiary deposits of the adjacent valleys occupying the crest of a spur to the east of the johnnie mine and close to the base of the lateral ridges of the spring mountain range are enormous deposits of facetted facet ted boulders principally of the harder rocks of the main range such as quartz grits quartzite cherty lime stones etc looking southeast towards the mt charleston ridge these deposits are seen to recur at higher levels and following along the base of the foothills to the northwest errati cs are afe found such as those at the base of mt moser these evidences of a former glacier pe aa al 7 1 7 4 the johnnie aline and mill professor stirling said in part the rocks to which I 1 wish to draw your attention are situated within and around the area of the johnnie consolidated group of mines at an altitude of about feet above sea level on a spur trending westerly from the spring mountain range and close to the border of lincoln and nye counties nevada at this locality a series of somewhat cone shaped peaks mark the course of the w watershed ater shed dividing the pahrump and las vegas valleys the range culminates to the south in a high mountain peak at an altitude of feet above sea level known at mt charleston which is covered with snow snow for many many months in the year the western slopes of the spring mountain range are crossed by bands of quartzite are suggestive of climatic vicissitudes in this part of nevada during past times differing greatly from those now prevailing aling and may account for the distribution of the massive boulder deposits of the valleys by a pluvia tile period following the melting of the ice sheets in the valleys at the higher levels the remarkable down of the slopes of the foothills may be ascribed to glacier abrasions in many instances the limestone beds although mostly dark blue and highly crystalline are often somewhat brown in color and they illey are also often cherty and siliceous in some places they are coarsely granular in others compact or highly the granular varieties are generally irregularly mab massive sive or in thick beds the ch cherty erty beds pass over in places into a completely bilici fled fied mass or from a solid limestone to a calcareous shale three phases of were noticed 1 of original sandstones 2 plutonic quartz as residual silica from deep seated of plutonic rock of the pegmatite class lode iode matter the rocks of the johnnie district are remarkable mar kabIe in the character and extent of the to which they have been subjected in tracing round the outcrops of purple quartzite which are the most prominent features in the topography of the region the alteration processes are plainly seen subsequent to the plutonic quartz invasion a third period of fracturing took place cutting both of the previous classes of which has resulted in the production of the auriferous quartz lodes such lodes are evidently connected with profound earth movements and resultant L faul tings thus providing a passage for ascending metallic solutions the examination of the mineral structures L of the rocks in the johnnie nie district clearly demonstrate that the earth movements which produced the faulting and shattering of the rock masses were not restricted to one period of time such as that of the great movements which formed the main fault lines it is noticeable that it is either within the places where bodies of crushed quartz occur or within the fault zones that the richest auriferous contents of the lode are met with and mostly near the places where the lime stones or their representatives are intersected by the faults it is probable therefore that the solutions have permeated most readily along the lines of least resistance afforded by such crushed zones three phases of are represented in the area first a general which resulted in the beds of quartzite and altered lime stones second an invasion of the masses I 1 have designated plutonic pluton le quartz third auriferous lode quartz formed along fractures after the consolidation of the plutonic quart masses I 1 believe therefore that the of the sedimentary rocks of th the e district was caused principally by ascending highly heated solutions it must be borne in mind that the of the lime stones may be ascribed to other agencies within the zone of circulating meteoric water I 1 believe that the final fracturing of the altered sedimentary rocks such as the lime stones and gave rise to conditions resulting in the formation of the auriferous lodes the metallic contents of which ascended primarily under conditions and as an after effect of the plutonic invasion until reaching the zone of circulating cu lating atmospheric w waters ater S precipitation took place through commingling com mingling and diminished temperature and that as the surface was lowered by erosion the ore bodies originally igi nally formed at lower levels in this zone not only appear appeared cid near the surface but will still be found to recur at as deep levels as are likely to be reached in mining op orations erat ions |