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were iasnlled n lysitneters fo order and ao0ax the ett'laeit for mnl sulp ysa. Pvary <br />week, the.lysimaas wan fleshed wiiaimum of ddtrt volume of de• et m rsova <br />tbsideat pore water. Fhsahhsg and oolletxim of the sweat wa scads wit6m dot hots. The eE%emt <br />was filtered tad the dearial coodeoetaace <br />meaaaeed rn the fiaid. Samples wets aealymd <br />- wea~ty -~s~etup'rrtne <br />~. <br />A <br />~• <br />.~g <br />d <br />.~... <br />-~~...~~ <br />,. .. r <br />a <br />d <br />~ . . v • a <br />'~DYO~~~~tXl <br />tgure ~ -Water sanrratioa, Oxygen concmttation, <br />lid sulphide contem in proflla u bite D2 rtes th <br />lags discharge era (A) sad site D7 rasa the ail' <br />~)• <br />Est S0, . Prior b meeaoremmte, the <br />lysiateten wen flashed with 60 thins pan <br />volumes in order m limit the htfiaeace d the <br />feCtladYy solid phases, stuff u gypstrm <br />(C>.S0.2HrO) oa the sulphate oonceapratbas <br />moatmted duria= oxidation measutemest. <br />Dorian dta initial fiushitrg, thn tulphsrve <br />eoncatradoa sad the ooaduaivity is the t'hsh <br />water dropped m a level approaching that of <br />do-ionaed water (less than 0.01 ppm SOr). <br />The lydmam were loosely oovared m <br />prevent stilphue wataminsdoa From bal <br />ramtall that is atfecoed by locally devated Sot <br />feuds. <br />Time domain retlecmmeay t'PDtt, <br />Tektrotdx 1502R,C) was used b estimate the <br />wlumetric water coateat u 0.1 m intervab. <br />Drivrtype piezometers were 1naWled at sites <br />is order m evdutae temporal weer table <br />fluctuation. <br />Iabotamry smdla of pyrrhatite <br />o:idsdon is columns Give pnvioualy shown <br />that the oxygen coatataQdoa tun caaeepood <br />Wdi with fats meassred from rho release Of <br />sulphate !a leach water. Di$eceocra is the <br />value of oxidadon between the two estimate <br />were within 40% of mesa values (g). Tae <br />results of the field stadia provide strong <br />sttpporriog evidet-te m wggeat that the <br />oxygen aotrsumptioa method yields valves that <br />are comltcmt with expeetad spsml trmdi sad <br />with tartlclpued effecu d moot cover layers. The trsalp pt~eaeoted here show that wuet able depth can <br />brie a very infitrential effect on oxidation rues. Tha resnlt9 alw iadiasa that oxidation rata dearase <br />with hrcraming expostae time m the umosphere, Finsfiy, iacluaioa of a 8ne~graioed layer u little as 20 <br />rm thick can reduce oxidation rata by more than two orders of magnitude. <br />2% w ~ ~e re-Eaa oxygm~ ~ n d~eae~sed~ umospheric boa (20.9%) w leas than <br />upper ing xygm oonceaauloa with depth was due b <br />me apply of oxygen controlled by the difihsivtty of the tailings sad the uptake of oxygen by srdphide <br />mtidetion. At site D2, the depth to tlts water table was approxlmatdy 0.65 m sad low degree of <br />~atlon were observed Dear the surface (Figatt 3). Although the current dutrlbudoa of sulphide <br />1003 <br />