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Hlbbinq Minerals Fa~18-262-7328 Jan 29 '95.2333 P. 03 I. .. Ttic~data prrsented in figares.3:and 4.represe~s.a 21=week.period.of record for.13. samples. They small number of sahrples limits :the detail. in which the acid .generation-sulfur content relationship can be dcscrrbcd.. Tlie potential for acid generation inarascs:linearly with total sulfiu content up to a total'sulfur comet of 0.45 :or 0.6796 and is.more than an order of magnitude higher at a total sulfur cottteni of 0.92%. At some point in the intermediate range (bcrjwcen 0.45 % or 0.67 ~ and 0.9296 Sr) there is a discontinuity in the relationship between the .~ateiof acid generation and total sulfiir content. I[ is concluded that:bacteriaIIy catalyzed ferric iron oxidadon`of pyrite is h'kcly'for material with sulfa; contents greater thanor equal to 0.92 %. ;. Unavoidable uncertainty is iatroduced in extrapohititrg these data to the field.. As. discussed on' p:.27 of ~"Characterization of Waste..Rock'firom'the Proposed. Cresson Pit" (September 1994), "the actual. rates of chemical release per unit mass in the field are anticipated to be lower than, those observed in the laboratory.".However the l~gr~ss of rock to be disposed will limit this .benefit. Flrrthetmore, the rinse water. to rock ratio in the field will be low relative to that in the humidity cell tests, which will tee to ~.TM.ase drainage concetttrations in the field (I.apakko 199;4).. ,. . Refottnces .~ Iapakko, K. A. 1994. Comparison of Duhuh Cottrplex rock dissolution inthe laboratory and field. In Floc. for the International Land Arste~tion:and Mine Drainage Conference and the Thi><d International Conference on the :Abatement of.Acidic Drainage, p. 41928.. i i . Addendran For ?the humidity cell data the rate of pyrite oxidation can be approximated by the rate of sulfate release, which is roughly proportional to the sulfate concentration in drainage samples (since drainage volume~is relatively.constant). If is assumed that: sulfate release from other sources is uniformly low. The sulfate boncentration,a[ week 31. is selected to represent the rate of pyrite oxidatidn. The soluble sulfate salts on the rock surfaces have been virtually totally removed by this'Itime. Sine l) sulfide sulfur cottetates well with total strlfiu (figure 2A, "Characterization of Waste Rock from the Proposed Casson Pit"); and.2) almost all .of the sulfide is present as pyrite, the total sulfur consent is a rcasonatile indicator of pyrix content. Assuming that the pyrite surface arrz~ available •for reaction is proportional to the pyrite content, the rate of pyrite oxidation should be .proportional to the total sulfur convent. vsovs:~o~ _ 'I.