OPAL CREEK WILDERNESS AREA

This page maintained by

Dr. Pete Poston
Professor of Chemistry
Western Oregon University
345 N Monmouth Ave
Monmouth, OR 97361
503-838-8218

[Introduction] [pH Measurements][Eh/BOD Measurements][Metal/Conductivity Results][Links]
[Water Sampling][Jawbone Flats Mine Dump Sampling Curriculum Project]

Introduction [top]

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 and galena. Abundant amounts of crystalline, as well as disseminated, pyrite and chalcopyrite are present, along with small amounts of quartz and zeolite. Veins were observed at several adits, which contained brown stains of limonite 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⁺ + 2SO₄^2- + 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.

Stability Limits of H2O	Water is stable within a narrow region of Eh potentials. These regions of stability vary with pH. Under oxidizing conditions, water breaks down into O2; under strongly reducing conditions hydrogen gas is evolved. Inorganic geochemistry in the environment is constrained within these boundaries where water is stable.
Iron Eh-pH Diagram	Iron is principally found as the +2 ion under acidic and mildly oxidizing conditions. It is found as a hydroxide species at higher Eh's and pH's. For a pH of around 7, a measured Eh of 300 mV, and the ppm concentration of Fe as determined by Atomic Absorption (next section), iron exists as the Fe2+ ion. This region of the Eh-pH diagram illustrates however, that small changes can result in major shifts in iron between solution and "yellow-boy" precipitate.
Pyrite Eh-pH Diagram
Copper Eh-pH Diagram	Again, the waters here seem to be perched on the edge of precipitation. Malachite is a hydroxylated copper carbonate. The presence of this mineral in tailings material indicates basic, oxidizing conditions.

Metal/Conductivity Results [top]

Click here for a Table of Water Quality Standards.

PART I: Heavy Metals by Atomic Absorption Spectroscopy

Acceptable Limits:

Pb = 0.05 ppm, Cu = 1.0 ppm, Fe = 0.30 ppm, and Zn = 5 ppm.

Analysis Procedure

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.

Results:

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.

	Lead was undetectable at a level below about 0.800 ppm. The level of lead found at the Tailings Pile site is statistically insignificant.
	Copper was undetectable everywhere at our current blank level.
	Iron was detected above our detection limit of 0.400 ppm. The highest concentration was detected at the 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.

Links [top]

• Ruthmine - Abbreviated Preliminary Assessment
• USGS Mine Drainage Interest Group Home Page
• Acid Mine Drainage Chemistry
• Alkalinity
• USGS - Water Resources for Oregon
• USGS - Water Resources of the United States
• EPA - Western Ecology Division

Western Oregon University

Direct suggestions, comments, and questions about this page to Pete Poston, postonp@wou.edu