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This page reports the results of a student water quality study within the Opal Creek Wilderness Area. Water sampling is being carried out at the Ruth Mine portal, Battle Axe Creek, Merten's Mill, Opal Creek, and from the tailings pile remediation site near Jawbone Flats. Over the next few years, we hope to obtain complete data on pH, Eh, conductivity, water hardness, Fe, Cu, & Pb concentrations, dissolved oxygen, and fecal coliform.
The source for the following discussion is "Geology of Oregon", 4th Ed., E.L. Orr, W.N. Orr, and E.M. Baldwin, 1992, Kendall/Hunt Publishing Co., Debuque, Iowa
Oregon's mining districts within the Cascades are divided up into five principle regions (see map), the North Santiam District (where the Ruth Mine is located), the Quartzville District, the Blue River District, the Fall Creek District, and the Bohemia District. For a complete discription of the geology of these districts follow this Jawbone Flats link.
The ores generally occur in veins crosscutting older volcanic rocks of the High Cascades. The veins frequently contain breccia which has been hydrothermally altered by hot, circulating ore solutions. The temperatures of the ore solutions was in the 250-350 oF range. Ores in the North Santiam District yielded copper, zinc, lead, silver and gold since the District was discovered in the 1860's. In the early 1900's, the Ruth Mine was the largest producer. Most of the ore produced lead and zinc, although small amounts of gold and silver were also recovered. Recently (1980), the Amoco Minerals Company leased the claims and explored for copper.
Samples of ore
were taken from a nearby small tailings pile. The ore contains abundant
amounts of chlorite
apparantly caused by hydrothermal alteration. The ore contains significant
amounts of sphalerite
Abundant amounts of crystalline, as well as disseminated, pyrite
are present, along with small amounts of quartz
Veins were observed at several adits, which contained brown stains
and disseminated red hematite.
One sample of weathered ore contained malachite.
In a personal communication from Rick Streiff, an economic geologist
who worked in the mine during the 1980's, there is significant calcite
plus some dolomite
in the Ruth vein system also.
pH Measurements [top]
Normally mine drainage water is acidic due to the presence pyrite. Pyrite weathers to form iron oxide, sulfate, and hydrogen ions:
FeS2 + H2O + 7/2O2 --> Fe2+ + 2SO42- + 2H+
As the mine waters are neutralized by mixing with fresh waters the pH rises and Fe3+ hydrolyzes to Fe(OH)3, creating "yellow boy", a slimey yellow-brown precipitate on the bottoms of stream drainages. We observed some of this outside the mine portal and at the Tailings Pile remediation site.
It was a surprise
therefore, that the mine waters were actually slightly basic! In a
personal communication from Rick Streiff, an economic geologist who
worked in the mine during the 1980's, the reason the pH is neutral
to slightly basic is that there is significant calcite (CaCO3) plus
some Dolomite (CaMgCO3) in the Ruth vein system. These minerals act
as a buffer to any acid solutions.
Eh/BOD Measurements [top]
For an overview of Groundwater and Redox Potential, click here.
Metal/Conductivity Results [top]
Click here for
a Table of Water Quality Standards.
PART I: Heavy Metals by Atomic Absorption Spectroscopy
Pb = 0.05 ppm, Cu = 1.0 ppm, Fe = 0.30 ppm, and Zn = 5 ppm.
Samples were analyzed using Atomic Absorption Spectroscopy. An acetylene-air flame was used. All samples were treated with nitric acid as a preservative; microbiological activity was minimized by adding several milligrams of Boric Acid. Samples were analyzed using standard addition techniques. The blank was treated the same way as the samples.
Location description: Mill = Merten's Mill, Gener. = Water Generator, BA CR. = Battle Axe Creek above remediation site, Pool = above Opal Pool, Tail = rivulet flowing through remediation site.
PART II: Water Hardness & Conductivity Results [top]
Water hardness was measured onsite using a test kit. EDTA was used first to measure total Ca. Then Mg was masked using NaOH, and only Ca determined.
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