From Mineral News – June 2000
by Alan Goldstein
The Walker vein one of the most well-known mineralized veins within the area described as the Central Kentucky Fluorspar District (see Anderson et al, 1982; Currier, 1923; Fohs, 1907, 1913). It has never been a source of economic mineralization, unlike some of the others. The claim to fame is its collectibility and beautiful minerals available to collectors.
In brief, the Central Kentucky Fluorspar District, which cover all or parts of 16 counties is a typical Mississippi Valley type deposit. Unlike the Illinois – Kentucky Fluorspar District (see Goldstein, 1997), there are no significant bedding replacement type deposits. Most veins are associated with faults, which are very numerous. Over 125 veins are known with traces of barite according to Anderson, et al (1982).
Exposed within the Middle Ordovician Lexington Limestone sought by the Caldwell Stone Company, this locality lies on the southeast side of Danville, in Boyle Co., Kentucky. This vein was first documented by Robinson, (1931). It is actually part of a fault zone containing numerous veinlets in an area 200 feet wide and 2,000 feet long. The primary vein varies from as little as a few inches to nearly six feet wide (Anderson, et al, 1982). Collecting productivity varies with the width of the vein. The best mineralization occurs where the vein becomes cavernous.
Minerals have been sought by local collectors in this quarry for many years. More recently, this locality has become regionally known, with regular visitors from surrounding states. Some strata within the quarry contained rare fossils, but these areas have been removed by regular operations, although a collector found a distorted, but complete 3” (8 cm) Isotelus trilobite on the dumps above the quarry in April.
The mineralization is dominated by calcite and barite. The thickness of crystallized specimens on barite matrix can make for some pretty heavy specimens. During the February collecting trip, two specimens exceeding 100 pounds were obtained and the April trip netted a specimen which required a backhoe to load into the pick up. (How they got the specimen out I do not know!) In addition, a boulder weighing about 1000 pounds was collected in mid April and moved to the quarry office where it is prominently displayed on the front lawn. The writer has not studied this vein sufficiently to describe the mineral paragenesis, but Jolly & Heyl (1964) described the mineralization for the entire district. This article should be considered a preliminary report based on three collecting trips and observations of a number of specimens.
Barite appears to be early forming, but occurs in stages throughout the history of mineralization (Jolly & Heyl, 1964). This mineral forms massive veins. Where fissures occur, it may be collected in crystals, often forming plates and rosettes. Aggregates are composed of flat blades 犀利士 or thin pod-shaped crystals typically 3 mm – 1 cm long (photo 1). Large crystals (i.e. solitary blades) have not been observed by the writer or described in the literature. Crystals are usually white, but have been noted as pale blue. Barite crystals can be lustrous or chalky depending on the collecting area. It may be colored brown or black by bitumen, either as a light tar-light coating or as dark inclusions within massive specimens.
The most unusual specimens collected by the writer occur as parallel stalactitic aggregates, composed of stacks of 3 mm crystals neatly oriented like a deck of cards spread at a 45 degree angle. The aggregates are often sprinkled with purple fluorite cubes (photos 2, 3, and 4).
Calcite is probably the most abundant vein mineral. It occurs in various stages throughout the mineralization within the vein. Crystals are typically white or colorless, but may be pale lavender or pink. They are occasionally lustrous, but often have a silky luster due to some dissolution. Usually twinned, they are similar in form to those from the zinc deposits in Smith Co., Tennessee. Doubly terminated crystals are common, from one inch (2.5 cm) to six inches (15 cm). Terminations are razor sharp, making collecting with good, thick gloves a necessity.
Crystals are often associated with mud-filled cavities within the vein. These openings are often large and allow crystals to grow as much as two feet (60 cm) in length! One such crystal is in the collections of the Louisville Science Center, having been on display since 1985. (It will likely be taken off exhibit later this year when the new exhibit gallery will be created. It is uncertain whether it will be displayed in the future.) The April, 2000 collecting trip netted the author three crystals from between 14 and 18 inches (32 – 45 cm) in length. Unfortunately, most have some surface etching or were damaged by equipment before I found them.
One specimen contained white phantoms forming a “cap” (covering only the top growth of the calcite) on a localized patch of doubly terminated twinned crystals. The white inclusion lay a millimeter below a clear mineralization.
Chalcopyrite occurs as inclusions in calcite. They are usually thin wires oriented perpendicular to the faces of the calcite crystal. When cleaning barite specimens in HCl, as the calcite dissolves away, the illusive chalcopyrite can be seen. Occasionally it may be seen within transparent calcite crystals forming a zone few millimeters below the surface.
Fluorite is very common in the vein. Crystals are generally cubic, from a few millimeters to a centimeter across. Crystals above 1 cm are rare from this locality. Within the district, Jolly & Heyl (1964) report a paragensis starting with white to buff, followed by bluish, clear, and finally purple. The latter color is pale or lavender and may have a dark purple rim (photo 4). Within a lower portion of the vein, I collected optically transparent fluorite in 5 mm crystals on barite. Some had a curious modification on one corner of the cube. Some crystals we coated with smithsonite. The most recent collecting trip netted some amber to yellow crystals. Iron stains played a role in creating these atypical colored cubes (for this locality).
Smithsonite – this is the first published report of this mineral from the Walker Vein. It was collected in fair quantities in August, 1999. This late-forming mineral is associated with barite, decomposing sphalerite, fluorite and occasional etched calcite. Smithsonite is brown or yellow in color in botryoidal, boxwork and in microcrystals of a rhombohedral or scalenohedral habit. Occasionally sub-millimeter spheres and hemispheres are found. Yellow colored smithsonite occurs as tiny rhombs, presumably colored by greenockite, and is often associated with fossil broyozoans. Some microscopic crystal aggregates are associated with decomposing calcite. The calcite will look like parallel needles in the x-axis, while the adjacent smithsonite is growing in the y-axis!
Some of the most interest specimens consist barite crystals coated with a thin veneer of smithsonite, sometimes sprinked with microcrystals.
Sphalerite is an early forming mineral, occurring as blackish crystalline masses, usually in barite. Crystals or aggregates may be up to 5 inches (12.5 cm) across. Well-exposed sphalerite crystals are not common. Bill McKenzie collected an etched sphalerite crystal coated with either greenockite or cadmium-rich smithsonite in April. (Naturally, it was in a boulder that I let him work on after I decided to go elsewhere!)
Strontianite is a later forming mineral that occurs is scattered occurrences through the vein. Curiously, celestine has not been documented from this locality. It occurs as white puff-ball aggregates from 3 – 8 mm in diameter. Stronitanite may be scattered on calcite, barite or fluorite.
Cleaning the specimens
Specimens occurring in the mud-filled openings are best left alone and let the mud protect the specimen during transportation home. Specimens should be spread out and left to dry. At that time, the minerals can be blasted with a nozzled garden hose and the dried mud will pop off. Mud that does not come off immediately will with a second water blast a few minutes later. This prevents the gooey mud from being shoved into the microscopic cracks with a tooth brush.
Collecting at the Quarry
The owners of this family-run quarry have been gracious to let individuals and clubs collect here over the years. Collecting hours are on Saturday from 7:30 am til noon. If you are traveling any great distance to collect here, contact the quarry or local collectors to see if it is going to be worth the effort. Although the vein spans the entire quarry, accessibility is limited to only a portion. Mineralization is restricted to areas around the vein and the swarm of smaller veinlets. The most productive collecting is associated with the widest veins. As would be expected, quarry operations cover a large area and blasting through the vein does not occur regularly. Presently the vein is exposed on several benches which are adjacent to highwalls of about 40 – 50 feet, both above and below.
Addendum: In recent years (2010+) the quarrying has moved away from the vein and the vein itself has pinched according to my friends.
Anderson, W. H., Trace, R. D., and McGrain, P., 1982, Barite deposits of Kentucky:
Kentucky Geological Survey, Series XI, Bulletin 1, 56 p.
Currier, L.W., 1923, Fluorspar deposits of Kentucky: Kentucky Geological Survey,
Series 6, vol. 13, 198 p.
Fohs, F. J., 1907, Fluorspar deposits in Kentucky: Kentucky Geological Survey, Series
3, Bulletin 9, 296 p.
Fohs, F. J., 1913, Baryte deposits of Kentucky: Kentucky Geological Survey, Series
4, Bulletin v.1, p. 441 – 558.
Goldstein, A., 1997, Illinois – Kentucky Fluorite District, Mineralogical Record, vol. 28,
no. 1, p. 3 – 49.
Jolly, J. L. and Heyl, A. V., 1964, Mineral paragensis and zoning in the Central Kentucky
Mineral District: Economic Geology, v. 59, no. 4, p. 596 – 624.
Robinson, L. C., 1931, Vein deposits of central Kentucky: Kentucky Geological Survey, ser.
6, v. 41, p. 3 -127.