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Cinnabar Along the Oak Grove Fork of the Clackamas River

Last Updated: 22nd Jul 2009

By Bill Tompkins

Cinnabar Along the Oak Grove Fork of the Clackamas River,
Clackamas Co., Oregon
by Bill Tompkins

There are several old cinnabar mines along the Oak Grove Fork of the Clackamas River, just below the dam at Lake Harriet, Clackamas County, Oregon. This study is being made because the mines are in danger of being reclaimed due to water concerns downstream. Located in Secs. 4 and 5, T. 6 S., R. 7 E., along the south side of the river, the Kiggins Mines, the Nisbet Mines, and the Aimes-Bancroft Mines have been abandoned and many environmental groups want to see their demise.


Quicksilver, also known as mercury, has a unique combination of physical and chemical properties that make it very useful in the manufacture of many products in the chemical, industrial and military fields. Being the only metal that is liquid at room temperature has led to its use in thermometers, barometers and other gauges.
Mercury ( Hg ) is silvery white with a faint bluish tinge. Below its melting point of-38.87¡C, mercury is a white metallic solid, and above its boiling point of 357.58¡C, it is a colorless vapor. Other properties include high density, uniform volume expansion, high electrical conductivity, ability to alloy readily forming amalgams with many different metallic elements, high surface tension, chemical stability, and toxicity of most of its chemical compounds.
The principal ore for mercury is the red sulfide, cinnabar ( HgS ). Native mercury and, more rarely, metacinnabar, schwatzite, livingstonite, and the chlorides and oxychlorides of mercury, have been found in some Oregon deposits. These deposits are found mainly in regions of Tertiary and Quaternary orogeny and volcanism. The mercury minerals were deposited from hot mineralized waters. The hot solutions rose along faults and other zones of broken rock and the mercury minerals were deposited in fractures and voids. Mercury ore bodies probably formed nearer the surface and at lower temperatures than the ores of most other metals deposited from hydrothermal solutions, and few deposits extend to depths greater than a thousand feet.
Cinnabar has a high specific gravity and is resistant to chemical decomposition. It therefore tends to concentrate in alluvium along streams and slopes during the weathering of the host rock. Most quicksilver deposits were discovered by prospectors using a gold pan to trace cinnabar float to its source.
To obtain mercury from cinnabar, the ore is crushed and screened and then roasted. The mercury is released as vapor, then cooled in a condenser. The bulk of the mercury is obtained directly from the condenser. The soot from the condenser is also collected, mixed with lime, and then retorted to achieve a 95% recovery rate.
Mercury has been known since at least the 4th century B.C. and was used originally in religious ceremonies. Until the 16th century, consumption was small and mainly for medicinal or cosmetic purposes. Since then, large quantities have been used for the recovery of gold and silver in the amalgamation process. Since World War I, significant quantities of mercury have been used to manufacture explosives, drugs, electrical apparatus, and in instruments. In 1944, production began on the mercury dry cell battery, and this has been the principal use of mercury ever since. The mercury cell process to produce caustic soda and chlorine became widespread after World War II. Other uses for mercury include mechanical measuring devices, as a catalyst in the manufacture of plastics; and in paints, agricultural chemicals, and dental supplies.
Prior to l850, the bulk of the world's mercury came from only three mines: the Almaden in Spain, the Idria in Yugoslavia, and the Santa Barbara in Peru. ln 1868, the Monte Amiata district in Italy became a large producer. In the United States, production of mercury was small before the California gold rush. California has historically been the leading U.S. mercury producer, with smaller amounts coming from Nevada and Texas. In 1979, however, Nevada produced almost all of the U.S. output from two mines in the McDermitt district.
In Oregon, prior to 197O, roughly l08,000 flasks of quicksilver were produced, representing about 3% of the total U.S. output. Of that amount, almost all was after 1927. Over 90% of Oregon's production was contributed by only 5 mines: the Bonanza in Douglas Co.; Black Butte in Lane Co.; Horse Heaven in Jefferson Co.; and Bretz and Opalite in Malheur Co. The Bonanza was by far the largest producer, with an output of almost 40,000 flasks. ( A flask weighs 76 pounds. ). The much smaller mines along the Oak Grove Fork of the Clackamas River produced a total of about 300 flasks, so they were not large producers. They were mainly two-man operations that could be worked profitably during times of high prices.

Oak Grove Fork of the Clackamas River, Oregon

There are three groups of mines at the Oak Grove Fork locality. The furthest upstream, the Kiggins group, was claimed first in 1923, by George Nisbit. The next mine downstream, the Nisbet group, also known as the Oak Grove group, was claimed 2 years later. The Aimes-Bancroft group is located uphill from the Nisbet mines and was claimed after that.
In 1927, D.E Kiggins was given a one eighth interest in the claims and he and Nisbit worked as partners until 1938, when Nisbet gave his interest in the Vermilion group to Kiggins and took ownership of the Oak Grove group for himself. During the early years, ore was treated in a more or less continuous shaft-type furnace constructed by Nisbit in 1925 or 1926 To construct the furnace, Nisbet built a concrete wall across the open side of a chimney-like opening in a rock cliff. A wood-burning firebox was built into the bottom of the furnace by placing two large fire tiles in a roof shape across the inside of the furnace near the bottom. The fire tiles kept the ore mass from crushing out the wood fire and allowed the burned ore to pass on both sides, reuniting beneath the firebox. When the furnace was in operation on a continuous basis, a wheelbarrow-load of burned ore was withdrawn through a chute opening at the bottom and a charge of new ore was added from a hopper at the top. In 1939 a cylindrical shafttype furnace with a capacity of about 15 tons per day was erected on the Oak Grove group of claims.
From 1940 on, ownership of each mine group changed hands several times and now the area is not under claim by anyone.


All of the quicksilver deposits in Oregon occur in volcanic rocks of tertiary age. The deposits in the Oak Grove Fork area occur in veins filling fractures in Columbia River Basalt of middle Miocene age. Fissuring is generally northeasterly and southwesterly in direction with some minor branch fissures together with some horizontal friction. The work done has exposed fissures filled with banded calcite containing thin lines of cinnabar. The rock itself is dark gray to black. Structures range from columnar to blocky to massive, and the texture from fine-grained to glassy. In the mineralized area the basalt is cut by numerous calcite veinlets of random orientation. These veinlets increase in number near the larger mineralized veins.
Cinnabar occurs chiefly in fissure veins constituted mainly of banded calcite, although one of the most productive veins on the Nisbit claims consists principally of the low temperature zeolite stilbite. Cinnabar is also found as narrow fracture fillings in the basalt adjacent to the veins.
The cinnabar-bearing calcite veins explored by the workings range from about 6 inches to about 6 feet in width. Locally, the individual veins converge to form mineralized zones 10 to 15 feet wide. The calcite veins appear to have been introduced into open fractures in the basalt. Displacement along the fractures is evidently slight, although locally the basalt adjacent to the veins is brecciated and has been altered by hydrothermal solutions to a dark, gray-green rock which contains considerable clay and is locally stained by limonite.
The calcite veins commonly have a banded structure. The calcite is a mass of coalescing crystals (typically up to 1 centimeter in diameter) that have been deposited in successive stages, one band upon another, until the opening was completely filled. Open spaces between the terminal faces of one band of calcite and the base of the next, and also open spaces between some of the calcite crystals, are commonly filled with chalcedony containing felted mixtures of quartz; opal; a zeolite which is either heulandite or stilbite; calcite; and locally cinnabar, pyrite, jordisite, and ilsemannite. The mixture ranges in color from red to white to black, depending on which minerals are present.
In places, the zone of oxidation is pronounced. The calcite has been leached away, leaving the cinnabar intermixed in the remaining soil and rubble. A large part of the production at the Nisbit claim is said to have been made by hydraulicking rich residual material overlying the Sluice vein and the Oak Grove vein and recovering it in sluice boxes and a home-made shaking table. Because sloughed material and vegetation cover parts of the sluiced area, and because the reject from the concentrators went into the river and was carried away, there is little evidence of the amount of ore treated in this manner.

The Kiggins Mine

The first claims, made by Mr. Nisbit in 1923-23, were along the Vermilion Vein. There were a total of five lode claims in this group: the Vermilion Vein alongside the river, the Falls Vein which is actually in the riverbed, the Stope Vein, and two other unnamed veins. Adit No. 1 on the Vermilion vein produced the most cinnabar in this group of claims. All the workings are near the same altitude on the back edge of a river terrace. The Kiggins Mine includes 330 feet of drifts and stopes and about 200 feet of crosscuts divided among three adits.
The Vermilion vein is developed by three adits. The No. 1 adit explores the vein from the portal for 180 feet northwestward, at which point the vein dies out and ends against a steep, westward-dipping mineralized cross fault which shows both premineral and postmineral movement. Exploration north and west failed to discover the vein extension. The vein is irregularly mineralized with cinnabar for the entire distance, but only one ore chute contains mineable ore. This is near the portal of the No. 1 adit and extends downward to the No. 2 adit, with a pitch to the east of 50¡. The amount of cinnabar in the vein decreases westward. The thickness of the vein similarly decreases westward from a maximum of 4 feet at the portal of the No. 1 adit to less than 2 feet at the cross fault zone.
The southeast extension of the Vermilion vein is explored by No. 3 adit, 320 feet southeast of the No. 1 adit. The vein in this adit dips 35¡ northeastward and splits into two steeper diverging veins, only one of which is mineralized with cinnabar. Cinnabar in the vein decreases eastward from the portal. The part of the vein between the two adits lies at the base of the cliff and is covered by vegetation and numerous driftwood logs.
The Stope vein north of the No. 1 adit is stoped westward for 30 feet and upward for 17 feet. The vein is eight inches thick and assays about six pounds of quicksilver per ton of vein material. It probably joins the Vermilion vein at greater depth.
The Falls vein crops out in the channel of the Oak Grove Fork of the Clackamas River for a distance of 250 feet from a point a short distance downstream from the furnace to a point opposite the No. 3 adit. The vein is 18 to 24 inches thick and is nearly vertical. The river channel follows the vein, which erodes more easily than the enclosing basalt. As a result, the vein lies in a narrow trench 3 to 5 feet wide and 10 to 20 feet deep in the riverbed. Part of this vein was mined opposite the No. 3 adit, but work could be done only during low-water stages of the river or when the dam upstream released little water. Numerous boulders and blocks of cinnabar-bearing calcite are strewn for more than half a mile downstream as the result of erosion of this vein.
In 1940, an option was given on the Kiggins claims to Horse Heaven Mines, Inc. After driving adit No. 3 to what is apparently the intersection between the Falls vein and the Vermilion vein and finding only minor mineralization, Horse Heaven Mining Co. failed to exercise its option to lease the Kiggins group and the property reverted to its owner.

The Nisbit Mine

The Nisbit group was claimed two years after the Kiggins group and was originally called the Oak Grove group of claims. In 1940, these claims were leased to Oregon Quicksilver, Inc. and they produced 66 flasks from the Nisbit claims. No recorded production was made after 1943.
The Nisbit mine was developed by about 500 feet of underground workings distributed among five adits and an inclined shaft. There are also several open cuts. The Oak Grove vein is developed by two adits and a surface trench; the Sluice vein by an adit and a surface trench, the Ben vein by one adit and a small stope; and the Zeolite vein by an adit and inclined shaft, both caved, and by a stope only partially accessible. Most of the production of the mine has come from the Zeolite vein.
The Oak Grove vein strikes east, dips 70¡ to 80¡ N., and was explored for a horizontal distance of 100 feet and for a vertical distance of 100 feet by two adits and a surface trench. It ranges from 6 inches to 6 feet thick. At the west face of the lower adit, the Oak Grove vein consists of three shears, each of which is mineralized with cinnabar, calcite, and silica. The vein is of stoping width where these mineralized shears are near each other. ln the upper adit, the vein is a foot wide at the portal and well defined but it splits westward into three minor shears that diverge. The Oak Grove vein produced 5 flasks of quicksilver, mostly from the lower adit. The average grade of vein material mined is about 9 pounds of mercury per ton.
The Sluice vein strikes east and dips 30¡ to 50¡ N. It ranges from 6 inches to 2.5 feet in thickness, and probably joins the Oak Grove vein at about 20 feet below the upper Oak Grove adit. The vein was stoped for 50 feet along the strike of the vein and 20 feet up the dip from the drift. Production was probably about 10 flasks.
The Ben vein has an irregular ore body about 1 to 3 feet thick which follows the trace of the intersection of two faults. One fault strikes N. 60¡ E. and dips 15¡ NW. The other, which terminates the ore body on the west and partly caps the stope, strikes N. 40¡ W. and dips 55¡ SW. This fault is premineral, but a small amount of postmineral movement has occurred. The line of intersection of the two faults strikes N. 50¡ W. and dips 14¡ NW. Production from the stope is estimated at about 20 flasks.
The Zeolite vein strikes N. 5¡ E. and dips 22¡ E., averaging 2 feet thick. The enclosing basalt has been altered by hydrothermal solutions to a mealy, soft, limonite-stained clay, which has been mineralized a short distance from the vein so that the ore body averaged 3 to 4 feet thick. The stope is about 40 feet on the strike and 60 feet long on the dip of the vein. It was stoped nearly to the surface. The zeolite vein consists principally of the zeolite mineral stilbite, with smaller amounts of calcite and silica. Cinnabar occurs in the zeolite and calcite in stringers, seams, and interbanded streaks, in small pockets, and as disseminated material in the basalt near the vein.
To the east, the Zeolite vein ore body terminates against a fault which strikes N. 52¡ W. and dips 80¡ W to vertical. No accessible workings cross this fault, so the relationship between the vein and fault cannot be determined. The absence of major postmineral faulting in the area indicates that the steep fault is premineral and that the Zeolite vein was mineralized by solutions that rose up it. At least one small postmineral normal fault offsets the Zeolite vein. It strikes N. 30¡ E. and dips 65¡ NW. and displaces the vein 1.5 feet. Production from the Zeolite vein was probably about 100 flasks of quicksilver.
Cinnabar was also found and mined in the open cuts on the West vein, the Top Hole vein, and another unnamed vein. About 175 tons of ore were mined from the large open cut and 10 to 15 flasks of quicksilver were probably produced. The structure in these cuts is obscure, but the mineralization follows shear zones which may be the surface characteristic of calcite veins at greater depth. The basalt is highly weathered and altered to a structureless, soft, limonite-stained clay.

The Aimes-Bancroft Claims

Workings on the Aimes-Bancroft property consist of scattered open cuts, all of which are caved. Little information could be obtained from them. It is presumed they explore calcite veins that are similar to but not as well mineralized as those on the Nisbit and Kiggins properties.
The Aimes-Bancroft group of claims was located by A. G. Aimes, who had been hired by Nisbit to do surface trenching on the Oak Grove group of claims for annual assessment work. Aimes found cinnabar at the side line of the Oak Grove claim. The vein extended into the adjoining Clackamas claim, which Nisbit had located but had not recorded. Nisbit gave the Clackamas claims to Aimes and Kiggins. Aimes later acquired sole ownership of the claim and proceeded through the following years to locate other claims in the area. E. A. Bancroft later acquired an interest in the claim group. Production of 7 flasks from sorted high-grade ore was recorded in 1932. Ore was evidently treated in the crude furnace on the Vermilion claim. There is no record of any further production.
Four calcite veins 2 to 4 feet wide crop out in the river channel between the main workings of the Kiggins and Nisbit mines. The veins diverge slightly in attitude, but all of them strike northwest, three are vertical and the fourth dips steeply north. Small amounts of cinnabar have been observed in two of the veins.

The Dam at Lake Harriet and the Three Lynx Power Plant

The cinnabar mines along the Oak Grove Fork of the Clackamas River also interrelate with the dam at Lake Harriet and the power generating plant at Three Lynx. The dam at Lake Harriet, also called the Oak Grove Dam, was built by P.G.E. at about the same time the mines were claimed. The bulk of the water that would have run across the mines is instead diverted into a pipeline that leads from Lake Harriet to Frog Lake, about 6.5 miles away. The water then runs down slope to the Three Lynx power plant that produces electricity for use by P.G.E. customers. Without this pipeline, the mines would be flooded in times of high water runoff.


The cinnabar mines along the Oak Grove Fork of the Clackamas River, Oregon, have been a part of Clackamas County history since 1923. They are very scenic and contain some rare minerals and mineraloids. It is this writer's opinion that they should be available to interested parties instead of reclaimed and lost for future studies. If readers are interested in this site, they should find time to study it soon.


1. Brooks. H.C. "Quicksilver in Oregon", Oregon Dept. of Geology & Mineral Industries Bulletin #55. 223p. (1963).

2. Brooks, H.C. "Quicksilver Deposits in Oregon", Misc. Paper #15 (1971).

3. Brown, R.E. & Waters, A.C., "Quicksilver Deposits of the Bonanza-Nonpareil District, Douglas County, Oregon", USGS Bulletin 955-F, p. 225-251 (1951).

4. Brown, RE. et al. "Quicksilver Deposits of the Horse Heaven Mining District, Oregon", USGS Bulletin 969-E (1951).

5. Drake, H.J., "Mineral Facts and Problems", U.S. Dept. of the Interior, Bureau of Mines, Bulletin 671, p. 563-574 (1980)

6. Frederick. F.H. "The Aimes Mine", (August, 1943).

7. Frederick, F.H. "The Kiggins Mine", (AugusL 1943).

8. Frederick, F.H. "The Nisbit Mine", (August, 1943).

9. Staples, L. "Ilsemannite and Jordisite", Am. Min. 36, 609 (1951).

10. Wiliams, Howel & Compton, "Quicksilver Deposits of Steens Mountain & Pueblo Mountains, Southeast Oregon", USGS Bulletin No. 955-B, p. 19-60 (1953).

11. "Oregon Metal Mines Handbook", Bulletin No. 14-D, Northwest Oregon (1951).

Micro Probe Spring, 2001 Vol. IX, Number 3 pages 6 - 13

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