. _STRALASIAN FIISTORICAL ARCHAEOLOCY 16, 1998 rdon. In-Ground Ore-RoastingKilns on the Hauraki Goldfield, .4nAtlas . niversity CoromandelPeninsula. New Zealand taphy of , \ational P.R.MOORE' and N.A.RITCHIE2
This paper presents the results of a study of the in-ground gold ore-roasting kilns on the Hauraki gold ,tgs,1842. field, Coromandel Peninsula, North Island, New Zealand. Ore-roasting was restricted to this goldfield in New ietransfer Zealand. The study involved a review of the ore-roastingprocess, examination of historical accounts of the lia in the kilns and their operation, and recording, mapping and assessmentof all known kiln-sites. The history of ore- naeologt, roasting at each of theprincipal sites is related to the survivingfield remairc. Thepaper also incorporates an analysis of the kilns' design and operation. Some comparisow are made with similar gold ore treatmentsand ineteenth technolog,,on the Australian goldfields,partly to ascertainwhy someNew Zealand mining companiesadopted ;aeologt, ore-roasting at s time (1889-1898) long after it had largely been discontinued in Australia, where the heyday of ore-roasting was in the I860s. .c.&H. *:: :::lns of roasting(also called calcining,and occasionally the sameis in a raw or imperfectlyroasted condition. It is also .1History -r,:--:: ) as a metallurgicaltechnique are uncertain but it has a obvious that grinding machinery of every kind will perform its iin'Press, 1 a -'s:or) . For exampleit was reportedby DiodorusSiculus office more efficiently and perfectly', : :: :rptian-occupied Ethiopiasome 2000 yearsago: 'The Lock and more recently Gojak and Aller (1997:26)have : Wewsof - :-:€aiing earthwhich is hardest[quartz in this instance],they undertakenexperiments with quenching roasted quartz. Their i1-dney. ::-* : -- uith a hot fire, and when they have crumbledit this resultsshowed that it cangreatly increase friability andtherefore ,, r :i. conthuethe working of it by hand...'(Yorurg1970:65, appearsto be beneficial,but we havefound no reportsor evidence , ':: -i: {'16pbrey et al. 1998, 184). ofquenchingroasted auriferous quartz at Aushalasiankiln sites. -:: 3.-.mans(and possibly earlier civilisations) developed In fact, unlessit was donein a very controlledmanner, quenching ;:. " -,:'c-fuedbrick and masonrykilns for roastingmetallic is likely to havebeen counterproductive, given that the objective -: 1-.r :alcrning limestone. From their frst appearance,at of roastingwas to producea well dried andmore friable product - :::-- ' r :ousand yearsago, the constructionof kilns andtheir readyfor furth€rtreatments. : :": :,- :: operationhave changed little. Regularreferences to Facedwith hardrefractory ores giving poor retumsin relation rlications, -:: :---3ss as 'calcining' suggestthat both the technique to assayvalues, mining companiesin manyparts of the western ' !*:a a:rd the technology(roasting kilns) are adaptations world turnedto ore-roastinglast cenhrry. In theAmerican West, : : -:. :uch longer establishedpractice of burning lime in prior i Station', to the adoptionof reverbatoryfumaces, they seemto have ,:r.s- !:-i.tures.3 The adventof roastingkilns enabledmuch initially relied on the simple 'bonfre' (open heap)method for rnal and -r::- , -.-res to be processedand large ones were able to be roastingrefractory ores, but in Australasia(and possibly only in a ' -t i'l r-ilialll' continuously. Aushalasia),some companies constructed substantial roasting :.n of the - :-. :arual Gold: Its Occutence and Extraction,Lock kilns to alter the ore in desiredways and maximisethe returns , - niversity : . :1 , citedfwo benefitsgained from roastinggoldbearing from eachton of oreprocessed.T Obviously they had concluded -: '.:. ::: :rushing. The fust was to makeit morefriable so that the benefits of roasting (less wear and tear on crushing ' machinery and better recovery rates)outweighedany ..4rmidale :- " : -.i crushmore readily; the secondwas to achievethe ::' :: cf sulphides which hinder separationand disadvantagesassociated with the method.E ceedings, rl: * ;::-::r:r of gold particles. The extra friability of quartz Quartzroasting was widely canied out on the goldfieldsin r:-:::.: :', roastingwas mentioned as the reason why toll mills Victoria, Australia during the 1850s,but by the 1860s i Political - -' : :=::ries) in Bendigo,Victoria, Australia (in 1854) improvementsin crushingtechnology were begiruringto discredit 's and its * ::*:: :::J benveenroasted and unroastedquartz in their the process(Davey 1986). An inventoryof some2500 mining *' ;. & W.B. . : . -- a :::s. chargingabout one pound per ton lessfor roasted sitesin Victoriahas documented only 23 'quartzroasting sites'.e . --5:: :.:::-se it lessenedthe wear on theircrushing machinery In the absenceofantecedents elsewhere, it would appearthat . '- :- :':a -
46 xnmt eying eatest g one TABLE1: Summaryof informationon the Haurakikilns ry the Date(s)of Orecapacity (tors) St. Location No. of kilrs Periodof we Rebrerres ing were constrction (1) ted their ryanide rr@OSTOCK- 1894€ '1894-1897 t50l AJHR TLSI\,IAN 1895,1 896,1 897 {,rarBatake Climie& Straples 1983 icson the b course J\FTIIAAH 4 (1889) 1889,1 890, 1889-1 ilories.rt 902 50 AJHR $snl 10(18s0) 1895-6 100 1889,1891,1 894 nsmade 13( 1895€ 250? I 895,1896 lsvations McAra1988 ryesand t m-plus SL'TERTON c.1896 1896- 150 McAra1988 irnn tee- lbn e ground [y at the rETORI{ 1897 or 1898 1898-1 901 150 AJHR1898,1903 sred by fi!mrt McAra1988 stetched cinimum JFIFE 1890? [50] Downey1935 2 m long 6laraui Valley depth of 1996and I|#"-JKAURI 10 1895? 1896-1 899 200-250 AJHR1897 Slcral Valey Downey1935
FT -€N CROSS 2? 1893 't894-1899 60 AJHR1894,1895 ilhce.ri Valley d to the Twohill1987 atofthe s known r -fPct 4 1897? 1897-1 901 ? [s0-100]? AJHR1898 hitianga. lb-t\hfey Broadetal 1984 n-Waihi, rdteries. ..IFIFI|ERMONT 2 (18s4) 1894€ 1894-1 897 80 AJHR rs are in rfuun \laby 5 (18s6) 1895,1896,1897 tion; the Simpson1979 ry ofthe
lb ' Flgues in brackets are probablecapacities (see Table2).
,h( lr orosuuction and periodsof use of all known Hauraki dried, and the kiln emptiedready for anothercharge'.2r The lffi :s res€nted in Table 1. companyhad recentlyconstructed much largerkilns, saidto be 20 ft in diameterat the top and37 ft in depth,capable ofholding trEs'dti OlhihD 100tons of ore. With referenceto tresling the ore by the Cassel [cyanide]process the managerreported t'[r. ot. is first dried in lM L-mum.slaim 4f Waihi was worked from 1885by the Union openkilns 'tapering down to the bottom, where they arefinished I! 1889 the company erected a large plant for the 'G*!{.C" with a brick arch, have a door and an iron chute for discharging ift,inlt aod treatmentof ore. It includedfour .drying'kilns, the dried ore into trucks. Thesekilns are fust chargedwith wood fr frE omsructed on the Hauraki field: 'The ore, as it comes and ore in layers,each layer being about 5 ft apart. After the fiE db rriDe. is dumped into the kilns, and while it undergoes kiln is fully chargedthe wood is lighted,and after all beingbumt ft procss of dr,ving,it is partially calcined. The kilns ile of a up, about one half of the chargeis withdrawn - 50 tons- and a mr' funrn resemblinga lime-kiln.' After crushing (in Globe similar quantityof wet ore and fuewood addedon to the top of crushers)the company intended to further the 'treat the charge'. By this meansthe kilns werenever allowed to cool ft@ material ;ulrerised in a Howell revolving roasting down, andthere was alwayssufficient heat - * to ignite the fuewood, !" which was addedand mixed with the new charge.This method FMEEiEtT rhe Waihi G.M.C. begantoacquire claims inthe of drying the ore was much more fuel efficieit becausethere .pamimiing the Union Company'sholdings in 1894. A new was not a largebody of cold materialto heatup aswas the case drrfrinar mmpan!; the Union/Waihi, was establishedin which with the smallerkilns, which wereemptied at eachcharge. The fu gruc omxpan!'hada controlling interest.2o costof the firewoodused in the largekilns was about I shilling -!EEs I t9-l reportthe Mines Inspectordrew attentionto the and 6 penceper ton ofdried ore.22 ne- w :r:rcal in rhe openkilns which the Union/WaihiCo. was During 1894-95extensive additions were made to theUnion/ *-'9" qere ozd by :b. madein the shapeof an inverted cone,having Waihi mill. Thirty new stampswere installed and additionsmade ir rrru E:e bonom. from which the ore was drawn out when to the roasting-kilnsand cyanideplant.23 The following year
AA 'two new calcining-kilns, of a capacity of 250 tons, were constructed,making a total of 13 kilns in use, with an average capacifyof I 50 tons each'. The firewood for the kilns and engines was conveyedfrom the bushby a tram road. In that year 10484 tons of timber was consumed(in the kilns and boilers), the cost of the wood for the kilns being I shilling and 9 pence per ton of quartz. The total cost of roasting in 1894 was 3 shillings and I penny per ton.2a A rehospective report on the Union/Waihi battery statedthe total costsinvolved in processingone ton of ore (basedon a sampleof 40764tons) was $US7.291lton,of which $US0.045/tonwas spent on hansportingthe ore to the kilns and $US0.5I 6 was spenton roasting :.:(: eachton.25 An I 897 'holcs' surnmaryof the plant at the mins included '13 kilns, from 50 to 150 tons capacity' (note the contradictionwith the stated 4,i:' capacitiesin the I 894 report).26 -n--. In 1898the Union/Waihi G.M.C. was thinking of converting to wet-crushing. Although it was almostcertainly using its kilns, becauseit was still dry-crushing, they are not listed in the company's plant.27 Dry-crushing continued to be favoured becausethe ore, despiteusing the samesieve sizes,tended to crush more finely than by wet-crushing(Banks 1912:ll8). During 1899 the companybegan to convertto 'wet-stamping'.2E In 1901 the Waihi G.M.C. took over the Union-Waihi Company'sproperties (including the Silverton battery). The companynow had 330 headof stampsat its disposalin its three batteries(a huge stampingcapacity by world standards)and rapidly completedtheir conversionto 'wet-crushing.2eThe Mines Inspectornoted 'dry crushingwhich for severalyears was very generalin thenorthem goldfields [and had 'a very injurious effect on the men employedin the mills where it was carried on'] is now not practisedin New Zealand'.3o The adoptionof wet-crushing at the Waihi mill necessitatedconsiderable alterationsand additionsto the plant. Theseincluded the removal ofthe shedover the kilns which thereafterwere 'used as storage- Fig. 2: Plan and section through the Union/Waihi kilns. hoppersfor a reserveofore'.3r In a retrospectivepaper reviewing ore treatmentsat the Unior/Waihi mill, the company'smetallurgist stated 'that kiln havebeen laid end-on. drying and dry-crushinghad proven very satisfactoryin the early Underground accessto the kilns was from separatetunnels days (1890s) so long as the ore was practically free of base (A, B), one serying four of the kilns (1, 2, 9, 10), the other sulphides;but if they were presenttrouble was experienced, providing accessonly to nos 7 and 8 @ig. 2). Kilns 3-6 must owing to the formationof solublesulphates while the orewas in havebeen accessed from a third tunnel (C), which presrunably the kilns' @anks l9l2:120). extendedfrom the now collapsedportal just southofthe other As this sunmary revealsthere are somecontradictions in the two. historicalrecords. They indicatethat therewere four dryingkilns Ventilation for the accesshrnnels was provided partly by in useon theUnion battery site in I 889.3, In 1890the number had narrow airshafts. Ctrriously, the airshaft besidekiln 7 opensout beenincreased to 10,each of 50 tons capacity,33although a later into the side of the kiln about 2 m from the top, rather than reportcontradicts this number.3a However,by 1894the Waihi extendingdirectly to the surface. A small, inclined shaft also G.M.C. had constructedan unstatednumber of larger kilns extendsfrom the side of kiln 5. No airshaftsfrom the third (probablyby modifring the earlierones), capable of holding 100 accesstunnel (C) have been located,althougfi a shaft (2 m x tonsof ore.35These were said to be '20 ft in diameterat the top and I m) at the rear of kiln I may have connectedwith that tunnel. 37 ft in depth' (i.e. about6 m by 11m deep- it is likely the latter By comparingour observationswith the historical recordsit figure is an enor and meantto be 27 ft, about 8 m). Two new would seem that the ten kilns still evident on the site are the calciningkilns, said to be of 250 tons capacity(each), were sameten that existedin 1890, and that they were enlargedin constructedin 1895-96making a total of 13kilns in use,'with an 1894to increasetheir capacityto 100tons. Enlargementofthe averagecapacity of 150tons each'(refer Table 1). original 50-tonkilns would explain why thereis so little space The Union kilns are located near the baseof Union Hill. betweenthem. However,all the kilns are now of similar size. Ten of the 13 historically recorded kilns are still clearly andthe reported diameter (6 m) doesnot agreewith their present identifiable,clustered together in two rows of five (Fig. 2). Two widths (average7.5 m). otherconical 'holes', situatedat a slightly lower level,may also If two of the four original (1889) kilns are representedby havebeen kilns originally (discussedbelow). the 'holes' which open into the main servicetunnels (A, B), it The main kilns range from 6.7 m to 8 m in diameter,and would explain their conical shape,why tunnel B has a second, appearto havebeen 8 to 8.5 m deep. Most arepartially infrlled obsoleteentrance, and possibly also the presenceofairshafts? with debris. The true depthsof only two (kilns 1,10)could be near the entranceto tunnel A. At their presentdepth (5-6 m) measured;they are 8.2 and 8.5 m deeprespectively. Four kilns theseholes 'are on the small side' for kilns, althoughifthe ground (nos l, 3, 6, l0) arecompletely or partly brickJined, althoughit level had beenlowered by at least3 m after they were abandoned, is possiblethat in some of the othersthe original brick lining thentheir original dimensionscould havebeen about 8 m deep has fallen away. In kiln I the brickwork extends up to about by 5.5 m wide. Thatwould makethem roughly the samesize as 3 m from the base. Above this level the walls appearto be the Jubileekilns (seebelow). ,tt plasteredwith concrete. Most unusually,the bricks in kiln 3 Assuming the two 'holes' are modifred kilns, then the ,{: 48 : -3stion remainsof where the other two were located. One point the dried ore is deliveredto hoppers,which in tum :. ssibility is that they were situatedjust to the east, and deliver it automaticallyto the rock-breaker.r6 - : sequentlyenlarged to becomekilns 7 and9. Thatwould mean During 1895 the WoodstockCompany erected a new 40- "J J '.\'estem :: two were abandonedand modified into ventilation headdry-crushing battery. The expandedoperation included the : .:s in 1890,during constructionof the additionaleight kilns excavationoftwo? furtherkilns (seePlate 1).3?The Woodstock -r 6.8. 10). C,'I battery was reported to be 'of the most modern type, working l- lAe locationof the two 250-ton or the three 150-tonkilns smoothly and well, which can be gatheredfrom the fact that the :/ :.'::rbed in historical recordsis not apparentbut it is possible ore is not touched from the time it is put into the kilns until it - ;:. '.\ere located just southof the otherten on an areaof now has frnished the entire course of the mill'.r8 However. the ", ::sedground. Woodstockmine managersand shareholderswere far from happy with the low percentageof the gold the mill was recoveringfrom ,e:,,dstock-Talisman (Karangahake) their ore. The Mines Inspectornoted: : - : :ISinception the WoodstockCompany experimented with Owing to its refractory characterconsiderable difficulty :::-.. :rocessesin aneffort to recovermore gold from thedifrcult has been experiencedin the fieafrnent of the Woodstock -:, :. :heir claim. The companywas one of the first (in 1894) ore,and many processes have been tried without success. .: - :: roastingas describedin this account: Dry-crushing [following roasting] with subsequent cyanide treahent, followed up by concentation and --:: fWoodstock]crushing plant includesdrying kilns, amalgama1i61,gave -:^:larin constructionto thoselately constructedby the the best results,but even then the ' extaction was comparatively low, and the consumption .;''' 1i Company....Dry crushingis resortedto...The kiln , : ft in depth,and 17 ft in diameteron top, having an of cyanide made milling operationscostly [almost certainly partly attributableto charcoalcontamination .:-;-snapedbottom, and is coveredwitha shed[the depth ,a-T ;-:: is incorrect]. The drying of the ore is continuous. from the roastingprocess absorbing the cyanidesolution]. : ::: a certainquantity is takenout at thebottom, more A start hasbeen made to crush wet with a dilute solution -: ". rre and frewood is placedon the top, and by this of cyanide in the mortar boxes, as an experiment, and :. =s the kiln is alwayskept full andburning. The kiln the bullion resultswere sohighly satisfactorythat it was ' . -: constructedon the side of a hill, a drive is put in decidedto adoptwet-crushing.3e r -- ie faceto its bottom, and by a tramwayfrom tlfs
:e tunnels te other ,l-6 must :sumably the other pafily by lpens out *her than :iaft also the third .t(2mx ir runnel. lecordsit :e are the Jargedin .entofthe nle space :ilar size, ru present
=nted by ,A. B), ir a second, :ushafts? r. (5-6m) :e ground radoned, I m deep ne sizeas ,: i:: ,: i j'i operatton, late 1890s(centre). Lltoodstockbattery at left. Note the stack offuelwood between the two kiln sheds (photo then the
49 River. Kilns l, 3 and 4 are still in good condition, but kiln 5 has Wood.tocL partialy brttcry collapsed. Kiln 2 has been filled in at some stage. .lt Either one or two of tle kilns (nos I and 2, Fig. 3) were constructed by 1894, coincident with the construction of the first Woodstock battery.a3TWo or tlree more were created in 1895-96.44_ . The battery was enlarged,and converted from dry to wet erushingin I 897, at which time ore-roastingwas probably terminated. By 1909 the shed covering kilns2-+ [ad been demolished. The Woodstock kilns are characterisedby their narrow V shapeand greaterdepth (up to 9.5 m) than thoie elsewhere.The lhlismqkiln, however,appears to have been somewhatlarger, although if it was loaded from the breach on its southwestsi- The Victoria batterywas constructedby the Waihi G.M.C. during 1896-1897 in order to process ore from its hugely productiv- MarthaMine at Waihi, 8 km to the east (McAra l9g-S). tramweJr to Woodatock workings I r .lt- Fig. 3: Planof the Woodstock-Talismankilns, Karangahatrc. I I I I *MccJ tunncl t- I Scctlo! ltlls l,8l .formerly In 1899it was reported tlat the [Woodstock] ore was freatedby roasting and dry crushing. This method, though giving a good extaction, was very costly'.4 The TalismanQeldmining Company,s battery was adjacent to the Woodstock Company's in the lower Waitawheta River gorge. Its single kiln (kiln 5, Fig. 3) was probably constructed in 1894 or 1895, in conjunction with the first Talisman battery. The ThlismanG.M.C. took over the Woodstockcompany in 1904 but had discontinuedroasting sometimein lg96 for several reasons: The ore is conveyed from the mine by aerial tramway, and delivered into the kiln formerly used for drying the ore and now used as a storage-hopper.From the kiln the ore goes to a rock breaker ... from which it is automatically fed into a revolving ore-drier. The use of this contrivance is a new departure for New Zealmd, 2 and is expectedto effect a considerablesaving in fue| to // -----n obviateloss ofcyanide causedby the presenceofcharcoal 11.,1 and partially carbonisedwood in ore dried by the kiln- (.1 ,tttqf process, and to prevent the fusion of fine particles of ) gold into globules on which cyanide solution cannot '-( i-- effectively act. ar The Talisman Company formally openedits new 50-stamp *e1-enrshing& ryanidingplant in July 1901. In the intervening years, 1896-1901, the revolving drying fumace, which made O51Om the company's kiln obsolete,was rqlorted to be working very 1,,.,t I satisfactorilyand processing 40 tons per day.a2 There were five kilns associatedwith the Woodstock and Talismanbatteries @ig. 3). They are locatedon the steephillside eastof the WaitawhetaRiver, nearits junction with the Ohinemuri Fig. 4: Plan and section through the Victoria kilns, Waikino. 50 rt ki,tn5 has !e stage. i_e.3) were non of the : fieated in rd from dry asprobably I had been : narrow v *tere. The rtat larger, hu'estside, ione of the iice tunnel this tunnel non to the bi'a small i. . . at Victoria battery inJantnry ' " :rtck ltning and entranceto the -: i at the rear 1 :: : -:iom @hotoby Lloyd Homer). r. Roasted i out at the er1;which lant.a5 LC.during rroductive 3). -:: a-s: :ecordedreference (in 1898) to kilns at the Victoria wide at the top. Early photos show they were coveredby an r :J:: i The kilns and rock-breakersEue situated on rising open-sidedtwin-gabled shedwith a louveredridgeline ventilator. -:e : ;:: r back of the battery ... After burning [the ore] is Study of dated photographs of the site indicate that this kiln : u* --1-.- :h -:'r r a g,v-ratorybreaker .. . in a separatebuilding, and shed was demolishedwithin a few vears of the cessationof :u::-: - ::cked to the stamps'.46Within a year the Mines roasting. :ri:e-- :: '.i questioningwhether ore roasting was a sustainable Ore ]trj r-:-,:::c- meansof treatingore: trucks were winched up to a turntable at the southem -:: endof the kilns, andthen eithertrucked along rails betweenthe :.-:s:ion of the future supplyof timber at the present rows of kilns (from whence the ore was dumped into the kilns), -1 -. : ;.ln5rmption is also a difficulty that will haveto or possibly the trucks were manoeuwedon rails acrossthe cente ',: j::: . The Waihi Companycut about5 acresevery of the kilns, in a fashionsimilar to that usedon somelime kiln .r': ::: ::\'. This, of course,is chiefly consumedin the operations.However, there is only one piece of possiblefield "' =:a ..iore. Whenit is pointedout that at theWaikino evidenceofthe latter system a vertically standinglength of -:::.-. :rrrne - there are six large kihs in constantuse, tram-line in kiln 8 which, although it appearssomewhat ::!: :-:.jrng 25 tons [seebelow], it may be imagined lightweight for the purpose, may have supported tracks across -::: : ::rsiderable quantity of timber is requiredto the top of the kiln. Obviously any track-supporting structure -, -: -.:-\ roastit.17 built over the kilns would havehad to havebeen substantial to : . -'.'. ue Victoria battery was completelyconverted to take the weight of loadedore trucks, and be madeof fairly fue ':----::,,r_i and roastingceased.48 The kilns arelocated on resistantmaterials. :: i : --:i: :oint of the Victoria battery site.4eThey were The roastedore was extractedfrom the kilns via a c.200m * -r: . :r;avated in 1897and first usedin January1898 long U-shapedaccess tunnel (Fig. 4). Having two entrances/ -.--. .:!! I il). Althoughthe historical reference mentions exits must havegreatly facilitated the loadingout of batchesof . :1: .::s rn constantuse', and only six aredepicted on roastedore from eachkiln and assistedventilation. Additional :r :,::r. nere is field evidenceof eight (Fig. 4), although ventilation was provided by a 37 m long side tunnel, a large -, : :33r !'ompletelyfilled in, possiblyprior to 1902.50 airshaft at the U-bend, arld 2 airshafts extending off a curious :: ::: s:\ are clusteredin two rows of three. Thev are * sideadit nearkilns 6 and7. Cablerunners in the tunnel suggest -r--r;r '-i tarl)'rvellpreserved (see Plate 2). that a haulagesystem supplemented human energy for moving -:: !::s rangefrom 8.5 to 9.5 m deepand average8 m the loadedore trucksthroush the tunnel. Jubilee (Waitekauri Valley) Kapai-Vermont (Kuaotunu) No historical account or photographs ofthe kilns on the Jubilee The Kapai-Vermontkilns arethe most northerly on the peirinsula, battery site are known. The Jubilee battery .around was erected and the only ones outside the Ohinemuri Aisilct l). fti 1889-90' 1935:215)but the fi$t @ig. @owney official referenceto company appearsto have opted for roasting becausethe gold it did not appearuntil 1892.5t The report makesno mention of was in minute particles. The kilns were conitructed in lg9?-5. any kilns butthey were presumably constructedabout that fime. qnlftrobablf used until late l89Z when the Kapai-Vermoni ft9 . kilns, originally reported by Broad et at. (19g4), are G.M.C. ceasedwork and went into liquidation.$ located on a n.urow ridge between two gullies, abbut l-j0 m The kilns are located in the upper Kuaotunu Valley below Aom the battery site. A small terrace (20 m x 14 m) has been StateHighway 25, ona moderately steephillside about 2SOm excavatedon one side ofthe ridge provide to a level area for north-northwest of the Kapai-Vermont low level adig them. the main gntancg to the mine (Fig. 5). The battery was situatedjust to There aretwo definite kilns, eachabout 5 m in diameterand the northwest. The kilns and their operation were descriLedby (originally) 8 m deep. A third pit only 2-3 m in diameter,but Simpson(1979). RecentlyMoorc et al (1996)presented a briJf partially collapsedand largely infilled, appearstoo mall to have accountof tlem together with a sketch plan. been a kiln.52 It may representan abandoned airshaft. A Reportsin I 894 and I 895 statethere were two kilns each 16 ventilation shaft(nowblocked) is locatedonthe southeastmargin ft in.dia_n9t9rat the top, with a depth of 27 ft, and capable of of the terrace. Underground accessto the kilns was via a tunnel treating70-80 tons of ore.s7By 1896there were .five kilns which probably extendedalong their [in eastemside and connected a row], with a capacltyfor holding 500 tons',5s altho,,ghanqtlier with the ventilation shaft mentioned above. The tunnel is now 1896report statesthat eachofthe 5 kilns held 80 tons olquartz.5e blocked by a roofcollapse a short distance in from the portal. From the size of the kilns (Fig. 5), it is likely they were of g0 Golden Cross (Waitekauri Valley) tonscapacity(see later). The sameyear the companyerected a revolvin-g furnace (rotary ore-drier)e similar in deiip to the Excavations for roasting kilns for the Golden Cross mine were one at the Luck-at-Last battery near Whangamata.ct According underwayin 1893.3 to Simpson (1979:52) tlree of the original kilns were infiilsd before the ore-drier was installed, but field evidence There aretwo kilns, construslsd 6n 3 5imilr principle to indicates only nvo were completely ffilled. those used by the Waihi Company, capable of holding Of the tbree remaining 60 tons ofore, and covered over by a shed ... [From thE kilns, two are still reasonablywell adit] the trucks arerun on to ahydraulic lift, rarhichraises pr.e-serve-{,bltth. third (no.3) has been largely infilled, partly them to the required level, so that the ore can be emptied with mullock. None ofthe kilns are brick-linea. fne sitebftll into the kiln. The ore is conveyed from the bottom of two completely infilled kilns is cleady identifiable, as a level the kilns to the battery building on tamway trucks... ra areawith a low earth rim on the westem side. Shallow grooves on this rim possibly mark the position of timber One definite kiln and the possible site of another were bearerswhich supportedthe revolving fumace. recordedby Twohill (1987). The obviouskiln is locatedon the hillside about 20 m above and 50 m northeastofthe old batterv Undergroundaccess to tle kilns was via a 25 m-long tunnel, site. This large pit has been excavated into steeply sloping ground,and is 8-10 m deepon its northem sidebufody 2-3 m deepon the southwestside. There is a double (forked) access- way into the pit on the lower southwest side, which must have beenused for either loading the kiln or removing the roastedore from it. The kiln is infills6 to within 0.5 m ofthe access-wav .base'. level, and is about7.5 m wide at its present A shallow depressionapproximately 6 m in diameteron level ground above the large pit may mark the site of the secondkiln. .it . Accordi.g to an 1894 report will be necessaryto again elevatethe roastedore from the outlet of the kilns to reachthe stone-breakerontopoftheplant'.ss However,whether the .outlet of the kilns' refers to a tunnel, or the opening on the southwest sideof the pit was not explained. It is not clear from tle presentterrain and historical records exactly how the kilns were loaded or discharged. An lg99 plan ofthe Golden Crosssettlement shows atamway extendingfrom the battery to the kilas, but no accesstunnel. The hamwav aliqrment forms a long curue,presumably in orderto gain altitude gradually, and appearsto have extendedto the open entance- way into the main kiln. Ore could have been elevatedfrom this point to chargethe kiln(s), but unloading roastedore from the samelevel would have been arduous and inefficient. Another possibility is that the roastedore was dischargedvia chutesinto the Kiln Crosscuttunnel which passedalmesf dfuestly beneath the kilns and continued on to the No. I shaft. The collapsed portal to this tunnel is situatedjust east of, and at alnost on the samelevel, asthe battery site. There is no evidenceof a ftamway extendingdirecfly from the portal to the battery althougha frestle may havespanned tlhe gap. The GoldenCross kilns were used until about 1899. Fig. 5: Plan and sections through the Kapai-Vermont kilns, Kuaottmu. 52 ?eninsul4 : l). The : the gold n 1894-5, -\'ermont .e1'below rut 250m , the main .edjust to sribed by :ed a brief s each16 :apableof : kilns [in $ another fquartz.5e iere of 80 erecteda ren to the {ccording re in{illed indicates :ably well .ed"partly siteofthe &sa level ',\ grooves ):e Kapai-Vermont battery site (foreground) and kiln shed (right), Iate 1890s (photo courtesy Auckland Public Library) ers which rg tunnel, ,'- .,,r -:-i::eJ *ith a service tunnel adjacent to kiln 3 (Fig. being lost to the elementswas a major concern. -: : r : iss mnnel is now blocked, but the service tunnel, The kiln site is shown on a 1926mining plan of the area. i: ' r--: L point ': ts still open. At the opposite where the ore There were four kilns on the St. Hippo claim, at two diflerent r:r .:.:i: :om "-i: the base of each kiln there are inclined locations. The two 'lower' kilns refenedto aboveare situated ':: ;: - ::-=::s. and there is a larger, vertical airshaft at the on the levelled crest of a narrow spur. Both have partially r: ,: i::-. : : : photographs -le service tunnel. Historical show collapsed,and arelargely infilled. The largerone is now about riiiliiiiri.lt: r -_:_.1 '.i 3:3 covered by a long shed @late 3). 6.5 m wide, while the otheris only 4.5 m across.Judging from b' um*n-rl:-" 1\ silsprrri Valley) the position of what is assumedto be the accesstunnel portal, their original depthmust havebeen no more than about6 m. - r : ::: :: :e \!'aitekauri battery in 1896 includes 'eight The two 'upper' kilns, originally recordedby Broad et al. , : :rr .r ]i,t rons capacity,and two, each of 200 tons (1984),are close to the upper St Hippo workings(see Moore e/ ,iriiilfu - $ probably --::'. ere constructed in I 895, after the al. 1996) and are much larger and better preserved. They are riirir,"--:.:---: :e:: :wchased by the Waitekawi G.M.C. This about l0 m in diameterand at least8 m deep,although because i r : ,. . :'.3: lhe Golden mine -: Cross at the sametime and their rims are lower on the north side,their useabledepth may '1iul - : : :: : : : there. by horse tramway, to the Waitekauri *t only have been5-6 m. Volume calculationssuggest each kiln r:iirLi:r.:* : ' .I :: -:e krlns was at the same level as the tamway. could haveheld 50-100 tons of ore. It seemslikely that these " .* i -:-: mill had been converted wet-crushing -: -'- to kilns wereconstructed first, to treatore from theupper workings, L,"r....- , --:'.:::rade the kilns redundant.63A map of the -: but their usewas discontinuedc. 1897 when the No.3 level (at a f, :::r, . : :r. ::3\\r n 1926, Shows a row of ten kilnS ", -,-:- On much lower elevation)began to be used as the main accessto luill :.: ::' _.:::i:e baftery. They arebelieved to have been the mine. The lower kilns were presumablybuilt in 1897-98to - :_: -i: avoid the needto elevateore to the kilns on the upper level. r' iri0':, \[.irrt,ltO \allel') Silverton (Waihi) ,, r : r-::-.: ::::rence to the St Hippo (or Waitekauri Three 150-tonkilns were constructedadjacent to the Silverton r:-.-i: 1 --,r:::3:s to the intentionto establishan aerial shaftabout 1896(McAra 1988:105).They have not been ':tff- , : "--:::_irhe need to sendthe ore by a ground -: -: relocatedand have probably been filled in. ":til:- : ------: ::-:::3io the kilns. a distanceof half a mile. ': 3/c iLlri:* : -: : . .: -: :, :e banery by aerial tramway for of a GraceDarling (Waitekauri Valley) ':r , j- ----: t :.: :s naintained,a rotary crusherwill be r*": -i- - - , ,-_-= -:.: r:e. savinga gooddeal of handlingand A brief 1894report on this mine states:'It is intendedto adopt '--. ,rLi: - - - ,- : n,-:s. $ hrch cannotbe worked in wet and dry crushing,which will necessitatedrying kilns to be made '': * :-.-t:- *i :: :: :seitherdamped,orthelighterportions beforecrushing is commenced'.65However, there is no evidence - : :. ':.:r,.li to the mill'.64 suggests of a kiln at the GraceDarling batterysite, and it seemsunlikely ,.:/aotunu. - This that iirr ' :-: - ':. ..:3::.rdthattheamountoffinermaterial that anywere constructed. 53 ANALYSISOX'THE KILNS Dcpth D ut! (Dctrc.l ii:lJ{ Designand C)peration n Despitethe voluminousamount of historic mining literatureon just about every aspectof chemical and mechanicalgold ]urt extraction technology, we are not aware of any reports which .O-r specificallydescribe how to build an ore-roasting vktorre tt {lr8 kiln, or the \ wooartocr. / bestway to operateone efficiently. \ Trllrmrr \ @!!! /o l!t[iilrt The Hauraki in-ground ore-roasting kilns vary from 8 to I 9.5 m deep and 5-8 m in diameter. They were generally t.-_"1 unlon/welht i ) ,/-- --- @llu excavatedby cutting into slopingground or levelling a ridge at "'2-9',2 a higher elevation than the crushing floor of the associated i r -- ,.,/ ,tCf-- rtr o-, ,,1@rll.:, batteries. The kilns have steepsides graduallytapering to a ;ubilcc roundedbase, and areopen at the top. i o_/ -; u!0!rl --i /' 'fior The Hatuaki kilns are ananged in either single or double '\J-' wlltil rows,with up to ten kilns in a row. Most werecovered by open- Krprl-VcrEoDt rlffii sided or partially enclosedsheds which would have provided shelterfor the kilnJoaders, contributedto the stability of the kiln walls by reducingground moisture, the efficiencyof their v operationby reducing heat loss, and dampnesseffecting the desiredend product- totally dry, heat-stessedore. mm ,i{l Both wet ore and frewood were loaded into the kilns from mm skips,which either ran along rails supportedacross the top of wtdth w $lllluil the kilns, or on tracksbeside or betweenthem. In small kilns lmctrcrl ,mru! the driedore was withdrawn as soon as all the wood hadbumed: Fig. 6: Dimensionsof theore-roasting kilns. Open synbols possible r{l5Dl the emptykiln was then reloaded.Larger kilns enabledthe ore- - meanvalues; symbols with vertical bars - minimumdepths. roastingprocess to be a continuousoperation, by toppingup the kilns with more raw ore and fuewood whenever a quantity of dl ri*{I' roastedore was withdrawn through the basalchutes.6 There 8 m and8.5 m deep. was sufficient heat in the kiln and the remaining load to igrite mt|x Thereis alsoconsiderable the new fuel and achievea satisfactoryroast. At the Union/ variationin the sizeofthe kilns at illsl the different sites. The Waihi battery continuousbatch production was achievedby Woodstock-Talismankilns vary quite mmr markedly in both depth and width, withdrawing about half of the roastedore every third day.67On whereasat the Union/Waihi site the kilns differ mainly thesefigures each batch of 50 tons was roastedfor six days. in width Gig. 6). In contrast,the Jubileekilns are remarkablysimilar in size. Clearly, and not Factors such as maintenancework on the kilns, clearing surprisingly,there is greatervariation in the dimensionswhere blockagesin the dischargechutes, and maintaininga desired i\ltfllill kilns wereconstructed at differenttimes (Woodstock-Talisman), ,.!ln throughputwould have govemedhow often and how many of or enlargedat a later stage(Union-Waihi). the kilns were worked at any one time. As expectedfrom their differing dimensions,the shapeof The roasted ore, dried and broken down but contaminated the kilns variesconsiderably. The Victoria kilns havedistinctly to some extent with ash and charcoal. was extracted from the U-shapedcross-sections, whereas some of the Woodstockkilns (sometimes baseof thekilns via narrowinclined chutes bricked) arealmost V-shaped (Fig. 7). The othersfit somewherebetween which openedinto undergroundservice tunnels. Therethe ore thesetwo extremes.There is also somevariation amongkilns J&il was loadedinto skips and truckedout to the crushers. at the samelocation, againmost noticeably at the Woodstock Ventilationwas providedby the servicetunnels and usually and Union/Waihi sites. In somekilns, for example,the upper 'n supplementedby air shaftsextending to the surface. The sides are nearly vertical (e.g. Fig. 7b), althoughthe majority anangementof these featuresis unique to each kiln site. In tapergradually towards the base. Possiblereasons for someof addition to helping to maintain the fues in the kilns, the air shafts thesedifferences in sizeand shape are considered in moredetail would haveprovided somefresh air and an elementof cooling below. for the underground kiln workers; even so, the heat, and the dustwhen the kilns werebeing discharged, must have been well Ore Capacity and Fuel Requirements nigh intolerable. Severalfactors make the calculationof 'kiln capacity'difficult. ilm{ Dimensionsand Shape Firstly, as outlined earlier,there are conflicting statementsin r@ the historic recordsabout the capacitiesof many of the kilns The dimensionsof the kilns were measuredat the Woodstock- and in some instancesno information at all. Secondly,the Talisman,Union/Waihi, Victoria, Jubilee,and KapalVermont diffrcultiesare compounded because no informationis provided batterysites. Some kilns couldnot be measuredbecause ofpartial as to whetherthe statedcapacities refer to the actual,optimum collapseof the sidesor significantinfilling. The lattermade the or maximum arnountsof ore eachkiln held, nor to the actual illfi measurementof maximum depthsdifficult, but they could be volumes of the chargesof ore and wood placed in each kiln establishedby determiningthe approximateheight befween the prior to 'firing up' or 'topping them up'. Thesedifficulties, of top of the kilns and the associatedaccess tururels, and making necessiryrequire some assumptions (outlined below), in order 'il someallowance for the ore chutes. to calculatethe 'probableoperating capacities' ofthe kitns. * Despiteerror in somemeasurements (up to about0.5 m for Rough calculationsof the volume of the kilns, and the depth and 0.3 m for width), there are obvious size groupings volumesthat would be occupiedby the ore (essentiallyquartz ml (Fig. 6). For example,the Woodstock-Talisman,Jubilee, and with minor sulphides,country rock, and clay) and fuelwood, tn Kapai-Vermontkilns aredistinctly nanowerthan the Union and enableus to estimatetheir likely ore capacity(Table 2). The *ilr Victoria kihs. The Woodstockkilns are also deeperthan most bulk densityof the ore loadedinto the kilns was probablyvery others,with depthsof up to 9.5 m. The majority are between similar to that processedfrom the modern opencastmine at 54 arfrr, i.e. 1.5-2 tonne/m3@. Mcleod, Waihi Gold Co. pers ;:rnm.). The volume occupiedby the fuelwood is more difficult :c qork out becauseit dependson what type it was, of what ar:: how it was stacked,and how thick the wood layers were. 5nrer-er, considering the types of wood likely to have been rsEd iD the kilns, an average density of 0.4 tonnes/m3seems nascnable @. Wallace pers comm.). Also, assumingthe logs ftt nsr t\ stackedin a lattice slangement, air cavities could have o\ rmrt 1rybetween 30Yo and 60% of the volume of wood layers, \ tuugi a figure of 40% is probably appropriate.6t I On the basis of these calculations, and accepting that the e.9)z mrm l-aien"fif'/nifrikilns had an ore capacity of 100 tons,6ethen tu "i-rctoriakilns probablyhad an ore capacityof 150-200tons, t ru tre Woodstock and Jubilee kilns most likely held 50-60 r@s urfor€ (Table 2). These are the estimatedquantities of ore tu Flns could hold at their initial loading, at a ratio of ore to mN. qrfaound 2:1 or 3:1. Although the Kapai-Vermontkilns rorr med to have had an ore capacity of 80 tons, that may rmi: reao possible only if the ratio of ore to wood was about >D lie rm6s11 of fuelwood used in the kilns is obviously a .rrrual t-actorin these calculations. According to McAra 'l'4f,t the 8 -::-<). Union kilns requiredone ton of wood for every ndth y um.:r :ne-but volume calculations indicate that 100 tons of ore IECTI -* - -rJ tons of wood (allowing 40o/ofor voids) would have or*r-:-ral fte kilns. A more likely figure is 45-50 tons ofwood, ssible M. gnts a ratio of approx. 2:l (Table2). h :896 ore production from the Martha Mine was about lE [|fitl short tons (38 700 tons), and in that year approximately .1ll0fXrl rrns of fuelwood was usedin the kilns andboilers (McAra -: l!91fiI I I r Assuming that at least 2000 tons of timber was c kiln531 wd. Ar $e boilers (a conservative quantity, based on figures Fig. 7: Shapesof the hilns: a Woodstockkiln 2; b - Jubilee kiln I, ry quite tiumilr-' . \ic-A,raI 988:93),then about 8500 tons must have been c - Uniott/Waihikiln l: d - Victoria kiln l. co/Waihi trast, the , and not TABLE2: CalculatedVolumes of Kilns, os where Orc,and Fuelwood rffiinr tlisman), nggl 91 Statedore Calculatedrolume Calculatedore Estimatedouantitv Estimatedratio of Probableore tnucrr€,'El capacity(tors) (m.)(1) rolunre(2) of woodtc fill kiln ore to ulood(4) capacity(tors) (3) "hapeof listinctly mtrT1s-lc6121 100-1 35 (501=30m3) (20t=70m3) (1.7-3) 50€0 rkkilns between ng kilns ]ll!ffiNri8.H 100 210-270 l00t=60m3 45t=160m3 1.8-2.2 100 rodstock hmr i1;ni : (AJHR1894) (av.240?) heupper 50F175m3 majority 55t=190m3 someof re detail ffifir: 290-320 (150t=90m3) (55t=190m3) (2.3-3.6) 150-200 (av.300?) (2001=120m3) (60t=210m3) (65t=225m3) fifEcult. ile**r$ 80 120-1 30 80t=70m3 20t=70m3 2.84 70€0 nents in UEffirr- ? (AJHR1897) 70t=40m3 25t=85m3 ie kilns : idly, the JlllLrtmr ? 100-1 20 (50t=30m3) (25t=85m3) (2) 50 rovided 6imum c actual lffitrlEs rch kiln '1ll'l1l ilties, of *u{r{Es :ac,E bd wirB formulaefor half banel (modified)and cy,linder+ cone. RarEe of vralues fu rdcril itreiri kih sizes and shapes,enors in measurement,dnd different in order methodsof calculation. ihs. lec r a€?g€ brik dersityof ore (1.75tonne/m3) ftom modernMartha Mine (D McLeod,V\Aihi didffi l: =r-r e 1 ton ore = 0.6m3approx Figures possible md the in brackeb are oie capacitids. -= {idr !'quartz lg$ 1' c€rcx a\,eragedensity_of 0.4 tonne@3Q1 wood likelyto haw been used (R \Ahllacepers comm) clwood, .uE {% b ocs e . tcn \,rood= 2.5m3(+40Yo). Possible qr,lantiti6sin brackets. 3). The iur sqlrros tr 1Ta cadirg of kiln onty. Possible figures in brackets. bly very mine at 55 consumedin the kilns. If thesefigures are correct,t}le overall Topography ratio of ore to wood usedin the kilns was around4.5:1. The main Union kilns were operatedon a continuousbasis. The topographyof eachsite must have had someinfluence upon andabout halfthe driedore (50 tons)was withdrawn every third the ultimate size and shapeof the kilns and the positioningof fr day,with another50 tons ofwet ore plus more wood being added accesstunnels and airshafts. The smaller, narrower kilns on top of the remaining load.72 The actual quantity oi wood (Woodstock,Jubilee, Kapai-Verrnont) were all locatedon steep ff addedis not stated,although only sufficientfuelwood to drv 50 hillsides. Obviously it would require far more effort, and tfl tons,not 100 tons, of ore at a time was required. At a ratio of expense,to excavatea platform for kilns on a steepslope than l:4.5 that would havebeen about 12 tons. Thatwould makethe on level ground,but becauseofthe terrainthere was often little kilns approx. 60yo f1rll,allowing for the volume occupiedby choice. On the otherhand, steep hillside locationsprovided an charcoalin the residualload, the smallerquantity ofwooa us.d, opportunity to excavatedeeper kilns and make better use of andreduced void spacesin thenewly addedwood layers because gravity. of probablerandom placementof logs. If wood were addedat Efficiency the sameratio as in the initial loading (i.e.2:l), then the kilns would havebeen 80 100% - full. We have no information on whether larger U-shapedkilns were The Victoria kilns were also usedcontinuously, with .each better at roasting ore tlan narrower V-shaped ones, but larger holding 25 tons [of timber]'.73 This presumablymeant that 25 kilas probablyrequired less fuelwood per ton of ore. Althorigh tons of fuelwoodwas addedeach time the kilns were reloaded. it is possiblethat any ofthe Hauraki kilns could havebeen worked So, assumingthe kilns held 150 tons of ore and that half the continuously,historical accountssuggest the largerkilns such load was withdrawn at a time (as at the Union kilns), then the asthose at the Union/Waihi and Victoria battery siteswere much ratio of ore to wood was about3 : I . In that casethe kilns would more suitablefor continuousproduction. Their greatervolume have operated70-80% full. However,it is possiblethat more and heat retentionenabled batches ofore to be roastedin less than 75 tons of ore was addedat the fust reloading- perhaps time. 125tons, which would meanthe Victoriakilns wereof 200 tons The availability and cost of fuelwood is likely to have had capacify.The ratio of ore to wood usedwould thenbe about4:l some bearing on the size and number of kilns which were (100 tons of ore plus 25 tons of wood added at subsequent constructed,and whether (as at the Union/Waihi battery) they reloading)and the kilns would haveoperated 80-90% full. were enlargsd at a later stage. At Waihi and Waikino large It is evident,then, that in a continuousroasting process much quantitiesof timber were availablefrom the nearbybush, and less fuelwood was required,with the ratio of ore to wood could be easilytransported to the kilns. In other areassuitable generallybeing between 3:1 and4:1.7a probably only in smaller, fuelwood,if not scarce,is likely to havebeen more difficult to intermittently operatedkilns, and in the initial loadins of obtain and expensiveto transport. This is one ofthe reasons continuously operating kilns, was a higher proportio; of why somecompanies replaced their kilns with rotary ore dryers.u fuelwoodnecessary. It would alsoseem that - with the possible .always Desiredor AnticipatedThroughput exceptionof the Woodstockkilns, which were kept full andbuming' in continuous - operationsthe kilns wereoperated The desiredor anticipatedthroughput ofore was undoubtedly about% fu11.75 an importantconsideration with regardto the numberand size nmn Obviouslythe variable amorurt offuelwood needed to operate ofthe kilns at eachsite. As documentedearlier the Union/Waihi thekilns couldalso explain some ofthe discrepanciesin reported Companyincreased both the number (eventually 13 in total) ]r-illj capacity. For instance,the main Union kilns could have held and the capacify-of their kilns over time as their ore exhaction fl1. 100or 150tons ofore, dependingon whatratioofore to wood increased.Similarly the Waihi G.M.C., which establishedthe was used, and what percentageof its maximum capacitythe Victoria battery knew it was dealingwith largeore bodiesand kiln was consideredto operateat efficiently. tn general,the would require a substantialroasting capacity, hence the t"*, statedcapacities cited in historicalrecords probably refer to the constructionofeight largekilns on the site (althoughonly six cptimum or usualoperating capacity, rather than the maximum appearto havebeen in continuoususe).7E amountof ore eachkiln could hold. Whether Ir the later Union Ore kihs had an operatingore capacity or maximum capacity of Chutes T_, 250 tons is unclear,but if the former,then they were probably 'lE! The ore chutesare an interestingfeafure in i)E:: thelargest kilns constructedon theHauraki gotdfield (along with themselvesbecause their designvaries somewhat thoseat the Waitekauribattery).76 betweenlocalities, and between :]ILN] L, kitns at the samesite. Although few of the i.lll mouths of the ore - Factors Influencing Kiln Design (Size and Shape) chutes(at the baseofthe kilns) arenow exposed,they werenot 't:]]r. l- always situatedat the lowest point. Somewere positionedto one side (e.g. Rock type and ground stability Woodstockkiln 3). The shapeand size of the ,-: openingalso varies considerably, from narrowand almost square The ore kilns were excavatedin variousrock types- ignimbrite (c.1.2m diam.,Victoria kiln 1) to moreopen and rounded (e.g. (a rock composedof pumiceand volcanic (Victoria, Union kiln l0). Some chute openingsare brick-lined, whili ash) Union/ ,,,':"'1 Waihi);andesite or dacite(Woodstocktalisman, Jubilee, Golden othersconsist of smoothedrock. it:i:: Cross,Waitekauri, St Hippo, Silverton?),and greyraacke (Kapai- Inside the servicefunnels, the end ofthe chutesare closed Vermont). Someofthe Hauraki kilns Mctoria andUnion/Waihi) by a gatemade from either a single solid steelplate, or by two .Ni '- were entirely or partially brick-lined, but the majority had plates,one fixed, the other moveable. The gate plates,raised :: t - exposedrock walls. Whetherlithology, or the degreeof fracturing andlowered by a leveror pulley,slid up and down in runnerson .:r. and weathering (hence likely stability) of the rock had any either side,usually made from short lengthsof tram or railway ,ix' 1 influenceon the size and shapeof kilns is difficult to assess.It track. Most gatesare about90 cm-1 m wide and I m high. '- ,u,,iiq. is notablethat the larger Victoria and Union kilns wereexcavated Virtually no two are identical. While they clearly operatedon in ignimbritewhich is relatively easyto dig by hand, and they the samegeneral principle, they tend to havea somewhatrough ltl :: arethe only oneswhich arebrick-lined. This may reflect some andindividual look aboutthem, probably owing to their regular concernaboutthe stability ofthe substrate,butthe Waihi G.M.C. bumingout (cf. fue grates)and periodically needing replacement "' (which ownedboth facilities) was a progressiveenterprise and or repairs.Their appearancesuggests scrap steel was routinely 'ill . riiiLL ". may havelined the kilns becauseit believedthis addedto their usedfor replacementparts or strengtheningthe gatesurround. thermalefficiency. Theore chutes generally slope at an angleof 40 to 45 degrees, 56 the kilns. Although ;e upon . the tipping systemdescribed above may havebeen lnique ning of to the Victoria battr;rykilns, it seemslikely that similar 'remote-coltolled' ,tipping r kilns systems,or long-handled tools' were used rn steep at other kiln-sites where ore-roastingwas a continuous process rn. and and it was too hot, smoky or dangerousfor the kiln_ loaders p€ than to work immediatelyabove the tuming tilns. en little CONCLUDINGCOMMENTS -rdedan ' use of By the time some of the mining companieson the Hauraki goldtield adoptedore-roasting in ttre 1890s( TableI ), theprocess was largely obsoletein Australia. While it may seemthat the New Zealand'ore-roasters' were about 40 yearsbenina the times, ls were they were, in effect, faced with the same problems that their r larger Aushaliancowrterparts had faceda few decidesearlier, i.e. rich -rhough refractoryores yielding poor retums. Ore-roastingwas expensive rvorked in terms of labour and fuel, but it was a proven iechnology, and rs such on the Hauraki goldfield abundanttimbir was readily avaiiable :emuch to fuel wood-firedkilns. lolume In plan andcross-section the Haurakikilas : in less closelyresemble the 'inverted bell-shaped'lime kilns describedin Ausfalian situationsby Pearson(1990:28-30), although the openingat the arehad baseofthe kilns for extractionof tle roastedore is more iimitar ,continuous .h were to that depictedin his diagramofa feed shaft-kiln,.7e 1) they The Hauraki ore kilns differ from their Australian counterparts, :o large in g-9 lolvever, that they are much larger, typically m Aeepand sh. and 6-7 m wide, and are all excavatedinto the gro-una. suitable As in Austalia, ore-roastingin New Zealandwas short-lived: Scultto and gate mechanism, Kapai-Vermont kitns (photo by no morethan sevenyears in most cases,principally reasons .- _ , *-rr,,rr*, becausethe adoptionofwet-crushing in themid-late i8gOsobviatea the need 4'ers.?? for pre-roasting(in Australia fuel shortagesand improvements in crushing methods,particularly the advent of eificient jaw ' . .:-. :..m about30 to 50 degrees(e.g. Woodstock kilns). The crushers,seem to have been the main contributors to its ubtedly ri::. : , : :e chutesseems to havedepended on how accuratelythe obsolescence).e :nd size : : .: kiln was lined up with position 'Jre the of the service Other factorsthat undoubtedlyhastened the demiseof ore- e'Waihi ;:-:: :..-r\\' it. In mOstplaceS the ChuteSare SunOUndedby roastingwere the ever-increasingcost of fuel as local supplies total) *' . i i :n. used -n to block up the original roughly hewn cavity. dwindled, growing appreciation that dry-crushing'and :action r ' - ,, "::: alsoused to line _the thechute roof and in somecases the handling dusty, kiln-dried ore were maior health haZards hed the i . : iapai-Vermont plate kiln 3, Fig. 5, see 4). (particularly by causing silicosis), and thi fact that residual iies and t,** \ charcoalin roastedore tendedto absorba portion ofthe expensive acethe LO.{DING TECHNOLOGY cyanidesolution used in the cyanideprocess. :nly six *-.:- *-,: :ourse of removing accumulatedrubbish from one The surviving ore-roastingpits on the Coromandelpeninsula . : " j-S ar rhe Victoria battery site recently,the Dept. of are an important example of early industrial technology, and : :-,::.--n $'ork crew found a set of reflect a unique response(one ofthe many highly . flangelesswheels. variible ore . : ::-::-lr. tnformationwas received (via J. Filkingtonpers. freatmentstried over the years)to the problem of extacting a l€cause :: : _: ar elderly man who said his father ,had worked higher percentageofthe gold from the hard refractory oresfoind Erween :r| -,:; :a: thewheels were a componentofthe systemwhich within the Hauraki goldfield. The early ore treafinentsfailed the ore ; - .: : : :: :rppingthe contentsof the trucks(ore or fuelwood) becausethe Ohinemuriores in the southernpart of the Hauraki .were i erenot : .: : . -s Nhenthey burning'. goldfield were characterisedby high clay, sutphiOesand silver onedto '.r content,all of which, more : : - : -i: e found no definitive informationor evidenceof often than not, were finely mixed : of the with the gold resulting poor : - -: ::chnologies',the informant's unverified description in gold recoveryin relationio assay ;!square values. ::: :- ,-:s! :soutlined here for therecord. :ed(e.g. Becauseit wastoo - -'; r.,-: loadersto pushthe trucksover the kilns, they Despitethe precedence of ore-roastingin Australia,we have :- rvhile , 'r- -: - t;: or otherwisemanipulated) out on tracksover the foundno documentedevidence that the Hiuraki mine managers ..:i":": -:: -ths. andtipped by meansof a hookattached to a drew directly on the ore-roastingexperience and techniques : closed ...r' : :r :i:l over the axle betweenthe flaneelesswheels. developedin Australia. Not only arethe Austlalian kilns much b1'two -:- r - :.-.:rsed insidepieces of angleiron iecured under smallerand differentin that for the most part they arenot built ;. raised : i ::--::_:i. and extendingthe full length of eachrow of in-ground,the rise and declineof ore-roaiting,aileast whereit - ..\ere rlefs on : --_::i two identicalsets). Apparently the hooks was most prevalent,in Victoria, appearsto have occurredfor railway . ':r' :: : : _.:::J to either side of the side_tippingrakeline substantiallydifferent reasonsand somethree decadesearlier :l high. -:. :3\ uere lodgedunder the rim, a quick upward (althoughat leastone kiln was operatingthere after 1900).sr eted on : :ippedthe -::.: contentsof the truckto eitherside However,as outlined,there is evidencethat during atrough r : , the late "' _- .:: x3\t truckwas then moved into position. The 1880sthe mining inspectors 'regular ';LL -: and some of the Hauraki mine .:: :.-::::rng trucksuSed by the Waihi GMC at th€ managers rcement ' looked to contemporaryAmerican experiencein - - ' .-:i. ::r e a u'ide flangeon the rim, so it conceivable .- treating refractoryores, and reachedthe conclusionthat pre_ rutinely :l.,., '-* : .-:::d hook would tip their contentsout. The roasting (coupled with dry-crushingand pan amalgamation) :round. - : " : :-..:::- :lat preventedthe trucks fromtipping whilst would greatly improve the recovery rates of the Ohinemuri legrees, - : : : , :: :eleasedbefore the trucks were movedover batteries.During 1888-89the Union G.M.C. constructedthe first kilns on the Hauraki field. Within about five years eight Supple pers. comm.; Parks Victoria, n.d. Inventory of other companiesfollowed suit. But 6s things tumed out their Mining Sites in Victoria. usewas to be short-lived becauseofthe generaladoption by the l0 pers. high industry of wet-crushing combined with the revolutionary Supple comm. The relatively incidence of kilns cyanideprocess in the late 1890s. in Victoria may be associatedwith the chlorination process which requires pre-roasting of ores. A development, the Even if wet-crushing and the cyanide processhad not been Newbury-Vautin chloriaation process,was widely adopted,wood-fired ore-roast''rg could only have been a short- used in Australia. The advent of term and increasingly expensivemeasure because the sourceof ore-roasting on the Australian goldfields the fuel for the kilns, the forests in th; vicinity, were bei'g in the 1850sand its possibleassociation with the consumedat an unsustainablerate (coal was not available as an chlorination processwarrants fi,rrtherinvestigation. altemative fuel until a railway was constructedto the mines in 11 Refractory ores are found elsewherein New Zealan{ most 1905). Regardlessof its efficiency as a teaheNr! ore-roasting notably on the WestCoast goldfields. Here, in the Inangahua had devastating long-term effects on the environmelrt around mines wet crushing was used from the outset even though the mines as evidenced by this statementto the l9l0 Royal less than 50% of the gold was recovered. Pers. comm. R. Commission into the silting and flooding of the Waihou- Hooker. Ohinemuri River system. The Waihi G.M.C. metallurgist stated: 12 '[We used] hundredsof thousandsof tons of firewood when we AJHR 1886C-4a p.12. were dry-crushing [and roasting]'. The loss of the bush had 13 AJHR 1888C-5 p.97. seriousramifications: 'We find the efect on our water power is 14 AJHR 1887C-5 p.24-26. this: A good rainfall in the old dayswould give us severalweeks of plenty of water, now it dies out in less than a week'.82 So, 15 AJHR 1887C-5 p.62. beyond the general environmental degradation caused by the 16 AJHR 1888C-5 p.97. destruction of the forests by the major mining sqmpanies 17 AJHR 1897 C-3ap.4. involved in roasting, its effects came back to haunt them long after they had ceasedthe practice and turned to more efficient I 8 Simpson(l 979),Broad et al ( I 984),Twohill ( I 982),McAra methodsof neating the ore. (1988),Ritchie (1990),Mcrrite et al 1996. 19 AJHR 1889 ACKNOWLEDGEMENTS C-2p.42. 20 Downey 1935'236. Thanks to Ray Supple (Parks Victoria), Denis Gojak 2l AJHR 1894C-3 p.45. (Archaeologist, NSW Parks and Wildlife Service), Peter Bell 22 AJHR 1894C-3 p.45. Slistorical Consultan! Adelaide), Mike Pearson(Canberra), and Andrew Wilson (University of Sydney)for providing information 23 AJHR 1895C-3ap.13. about kiln sites and ore-roasting in Austalia; Alastair Brickell 24 AJHR 1895C-3 p.63. (Consultant Geologist) for assistancewith the mapping of the 25 AJHR 1899 C-3 p.181 Essayby Mr A.H. Bromly on Kapai-Vermont site; Owen Wilkes for assistancewith the 'Treatment of Gold Ores in the Hauraki Peninsula', mapping of the Union/Waihi kilns and comments on drafts of originally publishedin this paper; Rod Wallace (University of Auckland), and Doreen the Engzneering and Mining Journal, New Mcleod (Waihi Gold Co.) for information. Also thanks to the York. The costs were cited in $US. Dept of Conservationfor the loan of multi-section tree-climbing 26 AJHR 1897C-3 p.91. ladderswhich enabled gain the writers to accessto and measure 27 AJHR 1899C-3ap.51. the kilns. 28 AJHR 1900C-3 p.88. NOTES 29 AJHR 1901C-3a p.86, AJHR 1902C3 p.38. AJHR p.4. I PhilMoore, PeninsulaResearch.P.O. Box 120,Waihi, New 30 1903C-3 Zealand. 3l AJHR 1903C-3 p.85. 2 Neville Ritchie, Departnent of Conservation,Private Bag 32 AJHR 1889C-2 p.42,McAra 1988:55. 3072,Hamilton, New Zealand. 33 AJHR l89l C-3p.42. 3 deBussy 197 | Yol.2.p.7 8, Kirk-OthmerI 984Vol. I 4, p.365. 34 AJHR 1895C-3 p.62. 4 The next major innovations, the developmentof rotary and 35 AJHR 1895C-3 p.45,McAra 1988:89. reverberatoryfumaces (both masonry and steel) arebeyond 36 AJHR 1895C-3 p.56. the scopeofthis paper. Thesemuchmore efficient 'roasters' differ in that the flames and heat generatedin the furnace 37 AJHR 1896C-3 p.68-69. arereflected by a lowroof platedownto ahearthwhere the 38 AJHR 1897C-3a p.5. (ores, placed material metal etc.) are and heated without 39 AJHR 1898C-3 p.67. coming into direct contact with the fuel. The major 40 AJHR 1897 p.68 problem advantagesof rotary and reverberatory fumaces are that C-3 opp. To resolve this the WoodstockCompany gradually fluxes can be readily added to the material to be roasted developeda complex strategy for mar 58 eotory of .r4' .{JHR 1898C-3ap.182. unpublished report to N.Z. Forest Service, Auckland 1- .{JHR 1898C-3a p.5. Conservancy. t ofkilns L! .\JHR 1903C-3 p.86. CLIMIE, N. S. & ST7^PLES,G. S. 1983.Karangahake: The o Process e: for a detailedplan of Yearsof Gold 1875-1935,Whakatane & District Historical oent, the the site seeMoore et al. 1996 Fig. 15.11. Society,Monograph 8. y usedin lustalian 5l -{JHR1898 C-3ap.5. de BUSSY,J. H. I 97 l. Materials and Tbchnologt,vol. 3 Metals and Ores, Longman Group, London. rwiththe : - -{JHR 1892 C-3ap.14. IL DAVEI C. :l ;i Broadet al.1984. J. 1986. 'The history and archaeolog5rof the North British Mine site, Maldon, Victoria', Australian Journal of nd, most .{JHR 1894C-3 p.44. nengahua Hist orical Archaeol ogt, 4:5I -56. -:.! _dJHR1895 C-3 p.59. a though DAVEY, C. J. 1996. 'The Origins of Victorian Mining mm. R. :: dXHR 1894c-3 p.44. Technology,I 85l - I 900', Artefact, 19:52-62. :,r .UIHR 1899C-3 p.45. DOWNEY J. F. 1935.Gold-Mines of theHauraki District,New :- UHR 1895C-3 p.39,AJHR 1896C-3 p.87. Zeal and, Governmentprinter, Wellington. :{ LT{R 1896C-3 p.37. GOJAK, D. & ALLEN, C. 1997.Hill End Historic Site euartz { 4JHR 1897C-3 p.50. Roasting Pits Complex: Conservationand Interpretation Plan, NSW NationalParks and Wildlife Service. nI r-TIR 1897C-3 p.50-51,Simpson 1979:46. HODGE, H. 1979.Frontiers of Gold: The Goldfietds Story. ftr. s€ \Ioore er al 1996Fig. 11.5. l85I -61, Book 2, CambarooraStar publications. penhurst. N.S.W. d r_aR 1899C_3p.6. ),McAra HIIMPHREY J. W., OLESON, J. p. and SIIERWOOD, A. N. ndr r_}1R 1898C-3a p.52. 1998. Greek and Roman Technologt: A Sourcebook, m r-m. 1894C-3 p.44. Routledge,London. nr r-H. 1895C-3 p.56. JARMAN, A. l9ll. 'Mining and ore teatuent at the Tblisman mine, Karangahake,N.Z.', rT r-aT. 1894C-3 p.45. T?ans.Awtralasian Institute of Mining Engineers16, Paper 232:339-385. dl :1,e Fsportion of voids is derived from actual stacking KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL :rrcrments using l0 cm-long, l0 mm-diameterwooden TECHNOLOGY 1984 Vol. 14, John Wiley & Sons,New n*eis and volume calculations. Someallowance needsto York. rc t*ie for the variablediameter of logs usedin the kilns, omly on mrl :-5_ttrationof voids by ore. LOCK, A. G. 1882.Gold, hs Occunenceand Extraction,E & rinsula', FN Spoon,London. ilrtl\ !-T-<. i89-t C-3 p.45. 'Journal, McARA, J. S. 1988.Gold Mining ''4$ t-8. tEgr c_3 p.50. at Waihi tB78-1952,Martha i| Press,Waihi, 2nd revisededition. r- tB96C-3 p.76. MOORE, P., RITCHIE, N. & HOMER L.1996. Coromandel a :t9a C-3 p.45. ^-T:-f. Gold: A Guide to the Historic Gotdfields of Coromandel r_tt*. -T .t98 C3a p.5. Peninsula,Dunmore Press, palmerston North. trlllt ls :re ro fuewood ratio is similar to what textbooks say PARKS VICTORIA n.d. Inventory of Mining Sites in Victoria. nrrn kilns 31d wood-fued brick kilns used.P. Bell. PEARSON, M. 1990. 'The lime industry in Australia- an !81$. :i-qm" overview',Australian Historical Archaeologt, g:2g-35. T .e_tF3.. t9i c3. p76. RITCHIE, N. A. 1990.A SurveyofHistoric Mining Sitesin rhe -Fr 4-iF3, - $96 C3. p76. Thamesand Ohinemuri areasofthe Hauraki goldfield, Dept. * .!-"trts of Conservation. -9ll C-3 p4l, Banks l9l2120. Hamilton. RHODES, 'il l_lEfl. -$98 C-3a-p5. D. 1968.Kilns: Design, Constructionand Operation, w, ''e. Chilton Book Co., Canada. nnrir. R-hodes1981 similar looking pottery kilns are pivately {@flmE5 '"rp'en-toppedup-draft' kilns SIMPSON,R. A. 1979.This is Kuaotunu, published, 2nd ed. iffi }8"=-, ^its5.Supplepers. comm. ---:c-*-c-ra- The Mining and SmeltingMagazine 1862 (cited in Gojak & tl{ill Purs n.d. Inventory of Mining Sites in Vctoria. Allen 1997). {lU r-:l[+"-i- - Cta p.202. YOUNG, O. E. 1970. WesternMining. An Informal Accountof rlem the Precious-Metals Prospecting, placering, Lode Mining and iomplex E qocp-1pp' Milling on the American Frontier Spanish Times to [c sizing from /893, University of Oklahomapress. r worked 4uffi. fi$:--i-- .Tppendices to the Journal of the House of ftqm:,el'zlr:. e-r -\nnual Mining Reports, Section C: Reports m 1lc hf,r5 $'ardeDs and Inspecting Engineers. hl{flrdtff.S.r I :a-:'\tilling and treatrnentattheWaihi Mine. " t- l--rry .l:.-rra/asian Institute of Mining Engineers 16, eur6------.-l$. u,,1 iltir- - a. lR.:]L\lO\D. M. & MILES, G. lgg4. Reporr rr ilc l:::-:.rdel Industrial Archaeology Team, 59