Show PROF ARTHUR LAKES ing irn prospects A v s up in mines and Minera 13 the kind of prospects the geologist is called on to examine and pronounce on are many and varied as are also the circum sta aces aces by which they are surrounded for example a party owns a ranch in a locality near which a young prospective mining district has been opened the ranch is of practically little value except as covering the site of a good spring and some fair grazing land for stock but the owner has perceived on it what he thinks are the same formations and the same mineral signs as are being developed in the surrounding district he sends for a geologist with the proper note nose for prospects to examine the land and pronounce on it whether its geological formations and conditions and its surface mineral indications warrant the expenditure of a certain amount of money in exploiting it before approaching the ranch in question it will be advantageous to visit the surrounding mining district study its geological formations especially those intimately associated with prospects opened on veins or ore deposits find out if possible what class of prospects and ores have proved successful or financially valuable etc then gradually as it were in concentric circles approach the ranch of virgin untried ground let us suppose then that the geologist has spent some days in thus cruising around and investigating the neighborhood and has now arrived on the ranch in question one of the first things to do is to climb some central or prominent hill in company with the owner who with a township to plat in hand 1 points out the natural or other landmarks marking the boundaries of the property the geologist from his perch takes in at a glance some of the main geological features of the ranch and also sees what sections of it he f had better tackle first and which seem most likely for ore signs and most accessible by trails or gulches thence The wilie makes a panoramic sli sketch etch locating on it by signs or letters such hills or areas as he thinks are by particular classes of rock e g on those by granite he places a G on his drawing such as appear to be by slates or sedimentary rock ar are marked by an S what from a distance look like dikes are marked D prospect holes by a cross and so on in these preliminary vegetation is often a useful guide the granite hills are generally covered by pine timber whilst the and slates may have a few quaking aspens ashens or be barren of trees but covered with short grass or sage brush outcrops of dikes or veins are often indicated by bushes growing on them if the ranch covers a very large area w for greater accuracy he may lo 10 locate c ate the above signs on the familiar township and section map of the owner commonly some local names assist him ailin indicating particular areas such as black mountain pov erty flat mineral hill etc the geologist locates on his drawing the points of the compass which usually correspond to some prominent mountain or landmark in the distance if the property properly is a very large one an accurate topographical survey may be necessary or a flat map made preparatory to a geological one but for general purposes on a small property if the geologist is a sketcher careful panoramic sketches taken from different points will answer most purposes for locating spots desirable for future exploitation having thus mapped out the course he is going to pursue the geologist and ranchman descend and systematically explore the country the geology of such localities may vary much in differ different eat regions 41 4 1 I 1 in n one it may be formations like those of leadville consisting of contacts of porphyry and limestone or it may be a granite region like gilpin county colo with fissure veins or one like cripple creek of eruptive rocks or a combination of eruptive rocks dikes and slates like that of B bellevue ell evue idaho for the purpose of illustration we may cite a locality we recently examined it was a stock ranch not far from the young mining districts of turret and whitehorn near salida calida colo before examining the ranch we spent two or three days in visiting the neighboring camps as well as the mines on cameron mountain adjoining the locality the general geology of the region between salida calida and these young mining districts is a very volcanic one it seems to be a northern extension of the great volcanic area which culminates south around cripple creek and has made mad e that camp so well known for its ore deposits A few miles east of salida calida and not far from the ranch in question are the relics of a ruined andesite crater volcanic dikes and flows of lava tuff and breccia abound A portion of the area is by the same sedimentary formations as at leadville viz cambrian quart silurian and carbon carboniferous lime stones and upper carboniferous and grits and a series of partially metamorphosed or slates which may be of precambrian pre cambrian or Algon klan age these sedimentary formations are intruded into by great masses of eruptive gran west k M 1 I 00 1 I ank av ac j 1 I 1 L nio ang N AND PANORAMIC VIEW OF prospecting FIELD ite some of this so called granite may be grano diorite or diorite dikes also occur of more recent porphyries ries and ande sites in the paleozoic formations and lime stones north of the ranch are the great bedded iron ore deposits of the calumet mine it is apparent to any one acquainted with mining geology that the signs and conditions we have described were geologically favorable for the occurrence of ore deposits but it sometimes happens that though all the proper geological tl conditions may be present in a region or locality there is little ore or not enough of sufficient grade or quantity to be profitable north and east of these striking geological features are the mineral veins of turret in fissures in granite or at contact with granite and dikes of igneous rocks immediately east of the ranch is mount cameron of so called it granite gra nite traversed by a system of parallel fissure veins striking approximately east and west and dipping steeply north A couple of miles southeast of this again is s the young mining camp camp of white horn characterized by a similar vein tern tem such then was the geological and mineralogical environment of the particular ranch we had come to examine and many of these favorable phenomena were represented on it the eruptive granite or grano diorite of mount cameron descended down into and formed the east boundary of the ranch this rock came in contact with a series of metamorphosed or slates whose steep dip of 50 to 75 degrees passing under the so called granite seemed a proof of the true eruptive or intrusive character of the latter otherwise the slates would have dipped off from the rock as do the sedimentary hogbacks hog backs from the granite range on the eastern foothills of colorado the lines of contact between the eruptive igneous rock and the sedimentary was clearly traceable for a distance of several thousand feet by a zone of oxidized and matter showing a honeycombed honey combed structure and occasional crystals of iron pyrite this contact locally named the denver contact seemed to us the most likely thing on the premises at the minnie moore mine in bellevue idaho a somewhat similar contact occurs between diorite and slate or carboniferous shale which has yielded several millions in lead and silver in the present instance values if any would probably be in gold this contact might be explored by an inclined shaft going down on the dip and lateral drifts driven each way north and south following the strike of the contact zone from the contact we crossed to an adjacent hill called mineral hill on this were a number of parallel veins having the general east and west strike characteristic of the region and dipping north these fissure veins if followed would intercept the denver contact A central and prominent view of the group was selected for a shaft to be sunk on it from which later cross cuts might be driven to cut and explore the other veins at a moderate depth thence we examined some prospect holes on poverty flat which proved to be an area by up tilted slates and crossed by numerous andesite dikes mineral signs should be looked for at contact with these dikes and if promising explored also by shafts the contact zones of the with the so called granite should be generally prospected in few cases on a property like this it is necessary to take many assay samples As we have explained in a previous article the results of such surface samples would be very misleading it is sufficient if the ex amiling geologist is satisfied that the various locations he has indicated show unmistakable signs of ore these geological conditions may warrant the expenditure pend iture of a moderate sum in general exploration here the geologists response ability ends he can in no case predict that exploration of such a property will prove a financial success or lead to great things he can only say that the geological surroundings roun dings and mineral signs are favorable and leave the rest to the grand chances of the prospecting field |