OCR Text |
Show HOW COPPER ORES FORM, Question Remains Unsolved in a Great Many Prominent Instances. There are not a few problems Jn economic eco-nomic geology that nre as vet unsolved, and are open for speculation. One of these Is the occurrence of impregnations of copper in purely sedimentary rooks unconnected un-connected with any visible or probable volcanic source or manifestation. Where did the copper come from, and how did it get whore we find it? When we find copper in Igneous or mctamorphlc rocks we attribute its origin, as of other motaliferou.s veins, to hot solutions associated asso-ciated with igneous or mctamorphlc agencies; agen-cies; but when such Impregnations, or copper ores, occur in purely sedimentary rocks without any obvious connection with volcanic or mctamorphlc agencies, we are somewhat nonplussed to account for their origin, says the Mining Reporter. Re-porter. Down on the Gila river in Arizona at a locality appropriately named Copper Mountain, we have seen a large area Impregnated with copper, usually In the secondary form of copper carbonate with Borne copper glance, or chalcocite. As those deposits occupy a highly volcanic center which probably was once a largo crater, and in which all the rocks nre of Igneous or volcanic origin, we readily attributed the copper to emanations of hot springs and fumaroles In the last stages of dying vulcanlsm- But when we find in the Green river bods of Wyoming Wyo-ming or of eastern Utah deposits of similar copper underlying large areas and lying evenly between beds of sedimentary rocks like a coal seam, with no trace of any ancient or modern volcanic agency In tho vicinity, or for hundreds of miles from the spot, wo nro at a loss to account ac-count for the copper. We have generally assumed that ultimate ulti-mate or original form of copper to "be copper sulphide, or copper pyrites, but. In these sedimentary deposits there is no trace of sulphide. The ores arc all of a secondary character, such as carbonates, oxides, or chalcocites. There are no fissures fis-sures or fissuro veins in tho vicinity, nnd the strata He as evenl horizontal and undistrubed ns they were when laid down by the waters of the vast tertiary lake thai once uovercd that Green river area for thousands of square miles. Again, we find in various regions the sedimentary red beds of the Jura Trias stained or Impregnated with copper sometimes sufficiently so as to constitute consti-tute a workablo ore. In some casos organic remains arc abundant in these rocks, and may have constituted a precipitating pre-cipitating agency for copper solutions; but, whence caso those solutions? There is no reason to believe that they percolated perco-lated from volcanic rocks that have long since been removed. In some cases, as In New Jersey, such sedimentary Impregnations Im-pregnations have been accounted for on the hypothesis of hot springs ascending from beneath and probably from a deep-lying deep-lying volcanic laccolite. or subterranean igneous magma. But in that region there are trappeon igneous rocks not far distant, dis-tant, also carrying copper. Such an hypothesis would hardly apply to a field like. that, or Green river. Can It be possible that certain seas or other large bodies of water could locally bo so charged with copper solutions, solu-tions, derived from somo unknown sulphide sul-phide source, ns to be capable of being precipitated by organic or other agencies to such an extent as subsequently to form beds of workable copper ore? It Is nn open question to invito geological discussion. |