WAIHI GOLDFIELD

Auckland Star, Volume LIII, Issue 143, 19 June 1922, Page 13

WAIHI GOLDFIELD

HEW GEOLOGICAL STJKVEY, i-nvrnEß prospecting AXA'OCATKI).

,„ t! „. -New Zealand .l.mrua! of Science ami Technology" appears a ;, r ,limn,,,;. report by Mr. I\ Ci. Morgan .Director «>i C.cologieal Survey), fur-ni-ti iTi_r some ilfta-ils- "f tbe re-survey of, Wiilii" .-. I i:i> Id. It i* explained that I ,1,1. ro-unoy was deemed advi-ablc lo j nsrertain if geological reasoning would I print to ll'«' l"v-,Mhi' nf bonanza ore bodies either at depth- or in .areas lalcriillv ..ui~i.lv tho -round ntread} explored. 'I'l-f "tea i'\umined during the .iirvev ••nn-'i-lcd of » belt of country p.vcrnl miles wide extending from Owaiaroa. live nii'e< wet of Waihi. to Waihi head', live mill".- to the oust. It is intriided tn make further underground rvtilorntii.il in tho Waihi and (irand .Inaction mine- before the main report 'j, linallv dra'tod After giving a Int. of woln.icat data the report states: 'In 1.,, middle tertiary t lines (some lllillioTi— of .vats a;;ol t!i'' Hauraki goldCel.l became I be scene of intense activity. A thick sheet of andesite nnd .[antic princimilly as la\a flows, but niirtlv in tlie form of ttttfs and breccias, were deposited upon a land surface consisting mainly of trins-jurn strnta. That the basement rock was above sea level ii a doubtful statement, but is inferred from the belief Hint tbe boils belonging to the older part of the Oamaru series at that time had probably boon elevated nnd in i |:,r - eroded, a- is seen in tbe ('nri)niani'.el district. After the outiiourir.j.'- ol the earlier andesit.es and (l_.iti.o-. colvnnic outbursts in tbe Waihi district at la-l ceased for a lon., time. It is certain tho land then stood at least 1000 feet higher above sea level than it does to-day. and it may bine boon 3000 ur _t)00 feet higher." The report further states that available indications point in tbe lodo formation occurring during tbe next period of igneous activity. Before the clone of the Miocene a new series of andesitic and ilneitic rock eruptions begun, giving rise to the rocks of f.'.e. Bersou Island series. Immediate!}' thereafter auriferous imart/. lodes were formed by ascending j heated solutions. Late in the Tertiary,: a third series of volcanic, eruptions J began. By thai time the eastern ex-' tension "I the Hauraki Peninsula had ' disappeared except for some outlying islands. Since then ihe land has been depressed some hundreds of foot below its presnt level. After that it seems to have been raised ill stages some hundred foot or more. DEVELOPMENTS AT DEPTH. The report states that the Martha lode may be expected to junction with the Empire in the eastern part of tbe mine at or even above No. 12 level and to tbe west, near Xo. 2 shaft at No. l:j level or lower. At or above 2000 feet the Martha lodo may also be expected to junction wit lithe Royal lode. Tho report adds: "Since in many places the Martha loiic is ruhbly, and manganese oxides arc plentiful, hope of secondary ore enrichment at greater depth may be entertained. More especially them is some likelihood of ore at the junction with the Empire, for that lode carries much colcite which is nn efficient prccipitent of gold. If tbe cnleite at this junction hag been leached, then the hope of secondary enrichment may be transferred to the Royal-Martha junction. Concerning the dEward lode, tho report states: "Tbri chance of secondary enrichment in dep_: i is fair, anil in addition or alternatively there is the possibility of bona__ primary ore." An important point of tlie report is _c reference to the Salmon crosscut by.tag driven at No. 11 level in a north-'-2st direction from the Edward lode. It is stated that several quartz veins have been intersected in this crosscut, one 12 inches wide assayed (SU/ per ton. The fact that the country is oxidised shows, states the report, that in a late geological period it was leached by descending surface waters, and if it should contain quartz lodes of any size, the probability of a secondary enriched bonanza at a somewhat lower level is considerable, nnd even great. OLD THEORY EXPLODED. In respeot to lateral prospecting, the report states the hypothesis that an intrusive mass of dacitie rock contains the principal ore deposits having been disproved, the probability of finding ore bodies by lateral exploration is much greater than was formerly thought to be the case. The exploration of the western side of the Martha Hill, where oxidised rock extends to the greatest depth yet reached in mining operations, is strongly recommended. The probability of payable and even bonanza ore at or near the horizon where the oxidised merges into the sulphide zone is considerable, and. states the report, may even hp great. POSSIBILITIES AT DEPTH. The report is hopeful as regards the possibility of discovering ore at depth in the Waihi district. It states: "In view of the geological history of the Waihi goldfield, and especially of its former elevation far above sea level, the existence of rich ore at a depth of 2000 feet is nut improbable, though it would lie too much to postulate a bonanza so rich and extensive as that of the Cp.lifornia and Consolidated Virginia." The report hae also this interesting summary: "The Waihi goldlicld has apparently reached the stage of old age, and tbe geologist has been asked to state whether its rejuvenation is possible. On the whole the verdict of the writer is favourable to the prolongation of the life of the field."