MINING GEOLOGICAL SURVEY.

Auckland Star, Volume XLV, Issue 70, 23 March 1914, Page 6

MINING GEOLOGICAL SURVEY.

AROHA SITBDIVISIOH. Br. J. HENDERSON'S REPORT. FUTURE OF KARANCAHAKE. The Department of Mines has just issued Bulletin .No. 10 of the Geological .Survey Branch of the Aroha subdivision of the Ha/uraki Fields, which contains a lot of valuable information, aud some is not of a very encouraging natuTe as far as the future of the Karangnhako district is concerned. This may perhaps, he the explanation of the sudden drop that took place in shares in the Talisman Consolidated Gold Mining Company la_t week, which was however followed" hv a fair recovery „n Saturday. When the . decline occurred, no information could he obtained of any reason for the fall in price as fa ra* recent developments in the mine were concerned. A*, a matter of fact, a cablegram was sent to the London ofiice of the Talisman Con- } solldated Company on Satur-vlv statin.* , that in So. 12 winze ore had been oh- ; tamed. value £1!) 12/0 per ton. in a lode ' Sft. in width, which mi doubt explained th« re.-oveTV in price of shares 11

referred to. Dr. J, Henderson's report probably refers to the future of the district. After going at a great length' into the lode formation and the deposition of the gold. Dr. Henderson states:—"lf the theory of ore formation advanced 'by the writer, be -accepted as a working hypothesis, the observed facto permit of conclusions more or leas definite. Large accumulations of ore will not be found in the continuation of the dominant fissures north of the WTaitawheta River into Tallica!.! hid. nor will ore be found in large quantities beyond the most Southern limit- of the ore as now determined. These conclusions are reached from the consideration of the topography. The greater portion of the rich sulphide bonanza of the Talisman mine has already been opened up. and the diminution of value in depth will 'be relatively abrupt. The conclusion is based on the high percentage of zinc showing in the lower portions of the ore body as now developed. . PROSPECTS OF DEEP MIX.NG. Referring to the persistence of lodes in depth on the Hauraki Peninsula, Dr. Henderson states: " In the majority of __.e_, wherever sufficient work has been done on the lodes -of the Hauraki Peninsula, it has 'been found that they either do not live down at all. or are much reduced in size, in depth." In support of this statement, the following illustrations are quoted.—The Crown ccrf. which averaged (say) 2 feet in width o\er a length of nearly TOfl feet in the Waiui- I w_eta level, contracts to a few >tringers in the crosscut from the Welcome lode, 500 feet below: Shepherd's reef in the Talisman mine, which in the No, 8 level W_is a rather irreoiilnr reef r_._n.p_. af

w_is a rather irrejruLar reef, becomeis at No. 12 'level, ..0(1 feet below, a brecciafilled fissure with no apparent veinlets of quartz or calcite. The great mas s of quartz. 40 feet or more in thickness, forming the crest of the hill over the Karanga-ia-ke railway- tunnel, dwindles to a few inches j n the railway tunnel, 800 feet below. At Te Aroha the great Buck reef at the end of the drive from Waiorongamai is only 12 feet thick, while on the hill above it average-- at least SO feet of quartz and silicise-,1 country. The Tokatea reef at Ooroma ndeJ. which in the outcrop is 30 to 150 feet in width, U represented in depth hy a fissure, carrying much mullock and clayey material and very little quartz. In "the Kapanga area. Coroman-del. the veins soiitract in width i;i the lower level.-. and become poor, in connection with tbe Thames area, mine workings have made it quite apparent that the vein fissures near thp'eurlace greatly exceed in number those nceunin" at Tcaicr depths. Many of the parallel veins amparently quite independent at or near the surface, on being followed downward terminate on the liaiigingiva!! 0 f the larger or more persistent reef.. At tt.uti iiitt:, :;i connection with the old 'j' ,' ii: .' '- : "c. mining developments hc.ow tne ..00 fcot level, moreover have gone to -hou that these -alcite bodies them_elve_ give out rapid!v in depth and give .place to rock exhibiting sheeted fracturing, numerous parallel joints narrow fissures, and pug-filled -battered > zones in which little or no calcite or i quartz has been deposited. At Waihi

_ __~ „,.,-_ u-puaiusu. __ v>aitH, however, in the deepest 10-vels opened, the lode filling continues downward _s strongly a s ever. Thus in nearly every district in the Hauraki Pemin_iii_ where mining operations have been .pushed to ; a considerable depth a tendency of the , lodes to decrease in mim'ber and ako in size has been noted. In the .summary of the economic possibilities of the Aroha subdivision the report states that the Karangahake area is a region where intense propylitizatlou --id marked topographical relief obtain. The two principal lodes traversing it have yielded gre-at quantities of bullion. In the Welcome lode the bottom of tbe rich bonanza sterns to have been reached, nor can it be expected that the rich sulphide ore of the Maria will attain depths much greater than those already explored. The other fissures of the district do not seem to have been such important circulation channel- _b the two just mentioned, and what ore they carry is likely to be confined to the higher regions. Most of the ore from beneath the Tuatan-i Hill ha.- iprobaib]'been already won. while southward from the .present workings, ii one may ju_j_e from surface conditions, the irrtensitv of propylitization rapidly diminishes. Dr. Henderson sums np the future of Te Aroha on _r__h the same lines, but adds: 'There is one otiher matter in connection with the Te Arolta OTea which deserves mention, and tiri- is the possible continuation down faulted be-

neath the Hat-. near Waioronjroma.. That th c country in whi. h the lodes are enclosed is continued downwards, down faulted beneath the plain. _ bigbly probable, and that portions of it downwards _Te propylitized there i ft no reason ho doubt, but that ore bodies cxiist is highly improbS-ble. For the ore bodie.of Te Aroha aTe only now in course of formation, and secondary ore deposition is not likely to occur under the conditions liere at present."