Link to USGS home page

Geochemistry of the Johnson River, Lake Clark National Park and Preserve, Alaska

By Timothy P. Brabets and James R. Riehle

Water-Resources Investigations Report 03-4252

Prepared in cooperation with the
National Park Service

This report is available as a pdf.


The Johnson River Basin, located in Lake Clark National Park and Preserve, drains an area of 96 square miles. A private inholding in the upper part of the basin contains a gold deposit that may be developed in the future. To establish a natural baseline to compare potential effects on water quality if development were to occur, the upper part of the Johnson River Basin was studied from 1999 to 2001 as part of a cooperative study with the National Park Service.

Two basic rock types occur within the drainage basin of the study: the Jurassic Talkeetna Formation of interbedded volcanic and volcaniclastic rocks, and the slightly younger plutonic rocks of the Aleutian-Alaska Ranges batholith. The Johnson River gold prospect reflects widespread, secondary mineralization and alteration of the Talkeetna Formation. Metals found at the prospect proper are: arsenic, cadmium, copper, gold, iron, lead, mercury, molybdenum, selenium, silver, and zinc.

The Johnson River prospect is located in the East Fork Ore Creek Basin, a 0.5 square mile watershed that is a tributary to the Johnson River. Water quality data from this stream reflect the mineralization of the basin and the highest concentrations of several trace elements and major ions of the water column were found in this stream. Presently, pH in this stream is normal, indicating that there is sufficient buffering capacity. At the Johnson River streamgage, which drains approximately 25 mi2 including the East Fork Ore Creek, concentrations of these constituents are significantly lower, reflecting the runoff from Johnson Glacier and Double Glacier, which account for approximately 75 percent of the total discharge.

Streambed concentrations of cadmium, lead, and zinc from East Fork Ore Creek and its receiving stream, Ore Creek, typically exceed concentrations where sediment dwelling organisms would be affected. Similar to the water column chemistry, concentrations of these elements are lower at the Johnson River streamgage, reflecting the fine sediment input from the glacier streams draining Johnson Glacier and Double Glacier. The amount of organic carbon present in the study area is relatively low and most sites indicate that some degree of toxicity is present even though these basins do not contain mineralized areas.

Acid based accounting tests on rock samples in the study area indicate a neutralizing capacity in the Talkeetna Formation rocks. These results should be used with caution because similar tests were not done on rocks from narrow veins or faults that could have acid generating potential. In addition, based on field tests during the study, carbonate-bearing rocks in streambeds are armored by a carbonate-depleted shell and would not readily neutralize acidic water.




Purpose and Scope


Description of study area

Methods of data collection and analysis

Bedrock Geology of the Johnson River study area

Geologic setting

Modifications to the geologic map

Flow and water-quality characteristics of the Johnson River


Specific Conductance


Water Temperature



Organic Carbon

Suspended Sediment

Geochemistry and Water Quality of the Study Area

Chemical composition and classification of rocks

Mineralization at the Johnson River Prospect

Alteration at the Johnson River Prospect and elsewhere in the study area

Discussion of geochemical data

Discussion of water-quality data

Summary and conclusions


This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

Download the full report (PDF, 3.4MB).

Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.

For more information about USGS activities in Anchorage Alaska, visit the USGS Anchorage Alaska District home page.

U.S. Department of the Interior, U.S. Geological Survey
Persistent URL:
Page Contact Information: Contact USGS
Last modified: Wednesday, December 07 2016, 01:23:27 PM
FirstGov button  Take Pride in America button