THE PROBABLE ORIGIN OF GOLD IN QUARTZ.

Thames Advertiser, Volume XX, Issue 6155, 24 July 1888, Page 3

THE PROBABLE ORIGIN OF GOLD IN QUARTZ.

CONTINUED, ( 'I'ntV deposition of gold from chloride solutions, refutes most emphatically the I popular notion that" gold doesn't grow." i The process of deposition is going on at ' the present time, and £[old does " grow " —often side by side with pyrites, These younger pyrites (probably always marcasite) decomposes very rapidly, even in dry places, and when removed from the mine. The gold and pyrites in the cavities of quartz and along the walls of lodes in most of our mines are the result of this later deposition. Turning to ihe difficult problem of the formation of lodes, Tho fissures ate, beyond a doubt, the consequences of mechanical causes, even if they have perhaps been essentially widened by the force of crystallisation of the mineral substances. The mineral matter forming tho lodes lias generally penetrated into the fissures from below, or from the country-rock, be it through solution from the immediate wall-rock, or from greater depths. In the great majority of lodes, it has not a'l penetrated at the same time, and certainly not in an igneous fluid condition, but as aqueous or gaseous solution. - Chiefly water, perhaps jn combination with numorous gases, <9as tba madicine, which the

Mattered particles of the metals and other substances absorbed them, and again deposited them in a far more concentrated form in the'fissureß, by a long continued process of precipitation, That is about all that can be said in a general manner, as an explanation' of the lodes. In detail thero still remains, it is true, much that is doubtful. The unequal distribution in the fißßures, the occasional symmetrically comed texture, and the composition of the lodes, varying to such an extent from that of the common rocks, all tend in the highest degree to show the correctness of the above explanation. Particularly striking and distinguishing in comparison with igneous rocks, is especially the rare, or very slight, amount of alkalies in the great majority of lodes, while their wall rock where it had contained alkalies, has frequently lost these for the most part iD the neighbourhood of the veins. They have been dissolved and carried off in solutions, while other substances have been precipitated from the solutions in their stead. The solution of the alkalies may often, re-acting, have aided the precipitation of the vein-materials, and it is therefore no wonder if it bo found that lodes are particularly rich between decomposed rocks; The decomposition through the solution of the alkalies, during the deposit of the I materials composing the lodes exerted a favorable influence on the precipitation. Had the decomposition, on the contrary, taken place before the formation of the lode, such a decomposed rock must have been unfavorable to the formation of the lode, partly from mechanical causes, and partly from the want of a re-action. Hence the local opp'osed conditions of the lodes between decomposed wall-rocks, Thus the formation of lodes shows itself to be not only possibly, but also probably, very manifold, and appears to have always stood in some conneotion with neighbouring, and often shortly before securing eruptions of ignous rocks. The local re-action of the ignious fluid interior of the earth created fissures, forced igneous fluid masses into many of the same, caused gaseous emanations and sublimation in others; and in addition, during long periods of time, impelled the circulation of heated water, which acted, dissolving at one point and again depositing the dissolved substances at another, dissolving new ones in their stead. The whole process is thus not confined to any particular geological period, but recurs at all times, either in the same or new reeions. So much on the general process of the formation of lodes, and the probable origin of gold in quartz,