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Research about Butte, Montana

Source-linked reports with geographic coverage including Butte, Montana.

6 recordsLinked to original sources
USGS2018

Two-event lode-ore deposition at Butte, USA: 40Ar/39Ar and U-Pb documentation of Ag-Au-polymetallic lodes overprinted by younger stockwork Cu-Mo ores and penecontemporaneous Cu lodes

The ore-genesis model for world-class deposits of the Butte mining district, Montana, USA, is deep pre-Main Stage porphyry Cu-Mo and overlying Main Stage Ag-Zn-Cu zoned-lode deposits, both of which formed from hydrothermal fluids driven by minor volumes of rhyolitic magma. The lode-specific model is that hydrothermal processes diminished in intensity outward from district center along lode veins, synchronously forming metal zones. The accepted models are controverted by new geologic and multi-method geochronologic studies. The new data reveal the following sequence of events: (1) Thermal study of country rock indicates that the 76.9-Ma Butte Granite cooled to 350–400 °C by 4 m.y. after emplacement. (2) Five quartz porphyry rhyolite dikes were emplaced at 67–65 Ma and another at 60 Ma (SHRIMP U-Pb) into the cooled Butte Granite without resetting 40 Ar/ 39 Ar ages in country rock. (3) Fifty-eight white mica and K-feldspar samples from alteration envelopes adjacent to Ag-Au-polymetallic lodes in outer parts of the district, Zn-rich lodes in intermediate parts, and Cu-rich lodes in the district center yield 40 Ar/ 39 Ar ages of 73–70 Ma for Ag-rich lodes, 65–64 Ma for Cu-rich lodes, and complex age spectra of 69–65 Ma for Zn-rich lodes. The data show that Ag-Au-polymetallic lodes occupied cross-district fractures by about 73 Ma, forming the greater Butte mining district. At 67–65 Ma, minor quartz porphyry dikes were emplaced into central and eastern parts of the rejuvenated fracture system but without evidence of related cupola or volcanic rocks or of thermal disturbance in the country rock. At 64.5 Ma, overlapping hydrothermal cells formed two stockwork Cu-Mo domes in deep parts of the fracture system. At 65–64 Ma and closely related to late-stage stockwork Cu-Mo activity, a penecontemporaneous hydrothermal pulse formed a high-sulfidation hydrothermal plume that (1) utilized the large re-opened fractures to cannibalize and remobilize Cu from autologous, stockwork, and older Ag-Au-polymetallic lodes, (2) deposited the rich, high-sulfidation Cu lodes, and (3) mobilized metals from early Ag-Au-polymetallic veins in middle parts of the district, transported the metals outward and redeposited them, enriching early veins, especially in the intermediate Zn plus Cu areas. Metals zones in lodes of the Butte district are the result of an intensely focused, Cu-rich hydrothermal plume that variably reworked the center of significantly larger, 10 m.y. older, Ag-Au-polymetallic lodes.

Montana↗
USGS2016

Effects of flow regime on metal concentrations and the attainment of water quality standards in a remediated stream reach, Butte, Montana

Low-flow synoptic sampling campaigns are often used as the primary tool to characterize watersheds affected by mining. Although such campaigns are an invaluable part of site characterization, investigations which focus solely on low-flow conditions may yield misleading results. The objective of this paper is to demonstrate this point and elucidate the mechanisms responsible for the release of metals during rainfall runoff. This objective is addressed using data from diel and synoptic sampling campaigns conducted over a two-day period. Low-flow synoptic sampling results indicate that concentrations of most constituents meet aquatic standards. This finding is in contrast to findings from a diel sampling campaign that captured dramatic increases in concentrations during rainfall runoff. Concentrations during the rising limb of the hydrograph were 2–23 times concentrations observed during synoptic sampling (most increases were >10-fold), remaining elevated during the receding limb of the hydrograph to produce a clockwise hysteresis loop. Hydrologic mechanisms responsible for the release of metals include increased transport due to resuspension of streambed solids, erosion of alluvial tailings, and overland flow. Rainfall also elevated the alluvial groundwater table and increased infiltration through the vadose zone, likely resulting in dissolution from alluvial tailings that were dry prior to the event.

Montana↗
USGS2015

Time scales of porphyry Cu deposit formation: insights from titanium diffusion in quartz

Porphyry dikes and hydrothermal veins from the porphyry Cu-Mo deposit at Butte, Montana, contain multiple generations of quartz that are distinct in scanning electron microscope-cathodoluminescence (SEM-CL) images and in Ti concentrations. A comparison of microprobe trace element profiles and maps to SEM-CL images shows that the concentration of Ti in quartz correlates positively with CL brightness but Al, K, and Fe do not. After calibrating CL brightness in relation to Ti concentration, we use the brightness gradient between different quartz generations as a proxy for Ti gradients that we model to determine time scales of quartz formation and cooling. Model results indicate that time scales of porphyry magma residence are ~1,000s of years and time scales from porphyry quartz phenocryst rim formation to porphyry dike injection and cooling are ~10s of years. Time scales for the formation and cooling of various generations of hydrothermal vein quartz range from 10s to 10,000s of years. These time scales are considerably shorter than the ~0.6 m.y. overall time frame for each porphyry-style mineralization pulse determined from isotopic studies at Butte, Montana. Simple heat conduction models provide a temporal reference point to compare chemical diffusion time scales, and we find that they support short dike and vein formation time scales. We interpret these relatively short time scales to indicate that the Butte porphyry deposit formed by short-lived episodes of hydrofracturing, dike injection, and vein formation, each with discrete thermal pulses, which repeated over the ~3 m.y. generation of the deposit.

Montana↗
USGS2012

Water-quality, bed-sediment, and biological data (October 2009 through September 2010) and statistical summaries of data for streams in the Clark Fork basin, Montana

Water, bed sediment, and biota were sampled in streams from Butte to near Missoula, Montana, as part of a monitoring program in the upper Clark Fork basin. The sampling program was conducted by the U.S. Geological Survey in cooperation with the U.S. Environmental Protection Agency to characterize aquatic resources in the Clark Fork basin of western Montana, with emphasis on trace elements associated with historic mining and smelting activities. Sampling sites were located on the Clark Fork and selected tributaries. Water samples were collected periodically at 20 sites from October 2009 through September 2010. Bed-sediment and biota samples were collected once at 13 sites during August 2010. This report presents the analytical results and quality-assurance data for water-quality, bed-sediment, and biota samples collected at sites from October 2009 through September 2010. Water-quality data include concentrations of selected major ions, trace elements, and suspended sediment. Turbidity was analyzed for water samples collected at the four sites where seasonal daily values of turbidity were being determined. Daily values of suspended-sediment concentration and suspended-sediment discharge were determined for four sites. Bed-sediment data include trace-element concentrations in the fine-grained fraction. Biological data include trace-element concentrations in whole-body tissue of aquatic benthic insects. Statistical summaries of water-quality, bed-sediment, and biological data for sites in the upper Clark Fork basin are provided for the period of record since 1985.

Montana↗
USGS2005

A 24 h investigation of the hydrogeochemistry of baseflow and stormwater in an urban area impacted by mining: Butte, Montana

Changes in water quality during a storm event were continuously monitored over a 24 h period at a single location along an urban stormwater drain in Butte, Montana. The Butte Metro Storm Drain (MSD) collects groundwater baseflow and stormwater draining Butte Hill, a densely populated site that has been severely impacted by 130 years of mining, milling, and smelting of copper-rich, polymetallic mineral deposits. On the afternoon of 26 June 2002, a heavy thunderstorm caused streamflow in the MSD to increase 100-fold, from 0·2 ft 3 s −1 to more than 20 ft 3 s −1 . Hourly discharge and water quality data were collected before, during, and following the storm. The most significant finding was that the calculated loads (grams per hour) of both dissolved and particulate copper passing down the MSD increased more than 100-fold in the first hour following the storm, and remained elevated over baseline conditions for the remainder of the study period. Other metals, such as zinc, cadmium, and manganese, showed a decrease in load from pre-storm to post-storm conditions. In addition to the large flush of copper, loads of soluble phosphorus increased during the storm, whereas dissolved oxygen dropped to low levels (<2 mg l −1 ). These results show that infrequent storm events in Butte have the potential to generate large volumes of runoff that exceed Montana water quality standards for acute exposure of aquatic life to copper, as well as depressed levels of dissolved oxygen. This study has important implications to ongoing reclamation activities in the upper Clark Fork Superfund site, particularly with respect to management of storm flow, and may be applicable to other watersheds impacted by mining activities.

Montana↗