| Show ELECTRIC prospecting FOR ORE IS THE LATEST THING IN MINING methods of electrical and electromagnetic prospecting prospect inor for under underground I 1 round mineral deposits recently developed in sweden h have ave been independently operated with success in several countries resulting in the discovery of a great number of ore bodies that were previously unknown and some of which have proved to be of great commercial value according cordin to hans lundberg 11 mining engineer new york in a paper presented at the meeting of the american institute of mining and metallurgical engineers in ill new york at this time by electrical prospecting ore bodies that 1 dj I not otherwise manifest themselves at the surface muriace may be e located stated mr lundberg 1 I conditions favorable to succeeds with the methods favorable geological conditions such a proportion of minerals of good electrical conductivity in the ore body as will render the matter materially a better conductor than the enclosing rock situation of the ore body within the range of influence of the electrical currents used and in ill proportion to this range a sufficient area of horizontal cross section of the ore body the result is to permit of spotting drill holes accurately and to save the expense of drilling barren ground 11 round the art of prospecting like other branches of milla mining i ing has developed rapidly durin during the last ten years mainly because of the advancement of mining geology and also because of the development of geophysical methods which are based on the different physical characters of minerals and rocks for example specific gravity elasticity and magnetic and electric properties these methods have proved of great value especially in countries where the rock is covered by soil and direct geologic investigation is out of the question basic features of methods employed in prospecting for ore bodies the methods based on studying differences in electrical conductivity have proved most successful for which reason the methods 0 of f electrical prospecting have been subject to the most energetic 21 and s systematic y s 1 work especially in sweden the great differences in the electrical properties especially in in conductivity between ore minerals and rock minerals are fundamental to all methods of electric prospecting for which reason the electrical conductivity of ore minerals and rock minerals has been carefully studied in connection with and previous to the development of the various methods of prospecting with electricity ore minerals with a me metallic callic luster such as iron pyrite galena pe cular iron magnetite etc also graphite and a number of coals have considerably higher conductivity than the surrounding rock and soil the methods of electrical prospecting may be divided into two principal groups po potential and cc electromagnetic b betic the potential methods which are the older are based on the investigation of the potential in an electrical field by tracing I 1 curves and measuring I 1 the differences in in pot potential estial between different points the electromagnetic methods are of more recent origin by them the direction and intensity of an electromagnetic field are investigated the potential methods were tried as early as about 1830 and came into greater practical use tise in 1918 in conjunction with the introduction of linear electrodes number of unknown ore bodies located the potential ineth methods have been used since 1918 at al about seventy ore deposits in sweden norway finland spain italy the united states and canada and resulted in the discovery of a number of ore bodies previously unknown some of these proved to be of great commercial value the area investigated exceeds acres the largest r and andio so far as execution is concerned most rational ea electric investigation vesti gation has been made in the region in northern sweden where acres have been ili investigated ted the scope of this investigation proves that a conla complete lete electrical investigation of an entire ore district is already possible from a technical as well as an economic point of 01 aei view i ei the ore bodies pyrite auriferous seno pyrite and zinc ore found by potential methods are divided into two large deposits kristineberg Kristi and B BJ jur 1101 foiS and several minor ones with a total area of about 1 square feet the electromagnetic methods for prospecting we were re first rs adopted about 1907 the main development occurred in 1971 11 l 1 when karl za a swedish mining engineer Z began begaii to experiment with a number of these ii methods they have a been used on oil a large scale and with good results since 1922 I 1 in prospecting in sweden and norway they are now nonbeing being exploited also in the united states and els elsewhere ethere in the tn elect electromagnetic roni agnatic methods current is caused to flow it in a ore body and the electromagnetic disturbances cause caused d by it 1 are examined when searching for ore bodies it must first be asce r be r bained whether the nature of the ore m minerals is likely to fuch cuch as to make the investigation successful T the lie decisive dec is factors are the specific conductivity the permeability abil ity and a inductance of the ore and of the surrounding rocks that is the electric and magnetic properties of the ore and the rock 9 which properties therefore should be examined in addition to this the geological conditions such as stratification the sequence of same the depth of the ore bearing horizon the extension of the ore bodies etc determine if the electrical investigation is at all possible further the method of investigation that would be more suitable must be ascertained in doubtful cases a laboratory investigation can be made on a small scale under conditions anal analogous offous to those expected in the field the field work should therefore be preceded by work in the laboratory |
