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CGBV GOLD MNG. CO • ID~719-589-:25a FE9 02'94 2313 Na.026 P.12 INTRODUCTION Mine drainage waters can carry significant loads of heave metals and other toxic elements, and thus can have severe adverse impact on surface-and gound•water quality. As a rssult thers have been significant efforss ova the years to pruiict the composition of thine drainage waters u'tat would n;sult from new mining projects. '1ltese efforts have Largely focused on stadc and kinetic laboratory tests using relatively small samples of oro and waste material (Ferguson and Morin, 1991). Uncertnirtties in the results of these engineering :esu can arise due to a number of factors (Ferguson and Morin. 1991), including whether. (1) the short time scales of laboratory-based studies can be extrapolated to make longer-term ptsdicdons; (2) the laborttory studies accurately reproduce geochemica! eondidons present !n the field, and: (3) the small sample sizes considered in laboratory tests ate truly representative of the larger-scale mineral deposit. Another approach to prcdicdng mine-drninage composidon thnt has received mttclt less attention over the years is acre that interprets the composiion of existing mint drainages in the context of various ttis such as ore deposit geology, climate, and mining methtxi. Wlldeman cs a1 (1 4) showed that the composition of waters draining mines in various Colorado From Range mining districts could be cortslated with ore deposit mineraloeY, and ccmcluded that pyrite content was the most dominant factor ceonaolling drainage composition. Wenu (1974) chazactenzcd the composition of different Colorado rivets affected by tread-mitre drainage, and wnsidercd to a limited extent the infhtenx of the geology and geochemistry of the minetaldeposin. In this paper we present n•,strlts of an ongoing empirical study of mine drainages in diverse ore deposit types in Colorado (Ficklin et a1..1992: Plutnlet: e[ al., 199?: Srttith et al., 1992: 5ntith ct aL, this volume). This study extends the results of those carried out by Wildetnart et rtl. (1974) and Wentz (1974), by evaluating a gtzater diversity of mineral deposit types arttl pta,^:^;^g in g<suer detail impot7attt geologic and geachemical consols on drainage composition. The results provide new insights into the dominant processes that control trnne- dtainage composltloa, and show that drainage cornposidon varies as a function of ore deposit ecology and the coining method used (underground vs. open-pit, eic.). Our interpretation of drainage composition data'in a geologic context is enabliigg us to develop improved predictive models for drainage composition that acs not corrtpttnrtised by non-representative sarrrple sire nr dmescale. These empirical models shotild dterefom Beady enhance current laboratory methods for the ptedicrion of drainage composition. Wears ctntsndy compiling data on drainage chemistry for a variety of other mineral deposit types and climates not found within Colorado (to be presented in Plumlee ec al., 1493), In order to make the predictive capabiliries of dds technique as broadly-applicable as possible. URE DEPOSIT GIiOLUGY We have evaluated mint and natural drainages froth a spectrum of ors deposit types in C:nlnrada containing a broad range of ore and gangue tttinenlogies, host rock lithologies, wallroek alteration, and trace eletttent siggnnttues (Fig. 1). Gwlogic characteristics of the deposit types sampled am presented in Table 1, arrd the drainages sarstpled ere listed acrtsding to deposit type in Table 2. Fur more dttaiied information about the gtology of these deposits, the reader is referttd to Davis and Strcufert (19917), and references contained tlterrin. SAMPLING AND ANALYTICAL METHODS At each drainage site, water samples were collected at the adit or drainage source; where passible, the drainages were also sampled at progressive distances downstroam At rach sample site. field measurements were made of pH, specific conductance, tcntperattus,