BUCKNER PEGMATITE AND ASSOCIATED POCKETS

MINING SEASON 2009, SMOKY HAWK

Photo Notes: Click on photos to enlarge. All photos are mine. Please credit appropriately if you use any.

Late 2008 and throughout 2009 it became apparent we had discovered an unusual pegmatite on the Smoky Hawk Mine. During 2008 a phenomenal pocket named the Smithsonian Pocket was recovered. Continued mining beyond this pegmatite and along two earlier pegmatites that had been continuously producing, led into a large, vertical pegmatite, apparently the source of several major pegmatites found on the Smoky Hawk.

This article discusses and shows some of the photographs of this "feeder" pegmatite, subsequently named the Buckner pegmatite in honor of one of the pioneer miners, John (Jack) O. Buckner, who developed many of the mines in the district, including the Two Point Mine. Mining will continue on the Buckner pegmatite this season; however, as you will learn from the description, it will likely be the end of these large pegmatites at this locality on the Smoky Hawk.

PEGMATITE AND MIAROLITIC CAVITY FORMATION

From the earliest days of mining on the Smoky Hawk, it was apparent that the pegmatites tended to form en echelon in parallel or nearly parallel planes. It was believed the horizontal pegmatites were related to vertical pegmatites or joints in the batholith, but direct evidence of this relationship was sketchy at best. Discovery of the Buckner pegmatite has solidified this observation. The parallel pegmatites we have been following for the past five years on the Smoky Hawk all branch off this main "feeder" pegmatite. The Buckner pegmatite extends from the northwest corner of the excavation at a dip of approximately 60 degrees. Numerous pegmatites, like branches on a tree, stem off this pegmatite, including two very large pegmatites at the deepest point, 60 feet below the surface.

The horizontal pegmatites we've been encountering at the Smoky Hawk, can be likened to wavy pancakes more or less stacked parallel to each other, some as close as 2 feet apart. As these pegmatites were mined, several vertical pegmatites were also encountered. Because these filled more rapidly with late-stage magma and cooled more quickly than the horizontal pegmatites, they tended to be unnoticed. Their crystal grain size, texture, and color are often similar to the host granite. The vertical pegmatites appeared as "joints" when the decomposed granite sloughed away during mining. Close inspection showed that when one of these vertical pegmatites was followed, horizontal pegmatites were eventually encountered. This suggests the fluid rose rapidly into the vertical fractures and then, more slowly bled or pushed out into the horizontal fractures. Pocket formation tended to lie relatively close to, but not necessarily within, the vertical pegmatite. Unless we encountered a bend or other interruption in the horizontal fracture, no pocket formed. The vertical Buckner pegmatite has shown that generally, the first abrupt change, closest to the vertical pegmatite, hosted the largest pocket. The horizontal pegmatites also demonstrate a generally thinning in relationship to the distance from the vertical pegmatite, presumably due to the diminishment of magma. In a sense, the horizontal pegmatites can be likened to the branches of a tree spreading outward from a central trunk, although the "trunk" would actually be a few inches thick and several feet wide.

INITIAL INDICATIONS AND MINING UP TO THE BUCKNER PEGMATITE

Indications for the Buckner pegmatite had long been noticed from the red iron-stained rocks on the surface and a few microcline and smoky quartz crystals. It was not excavated because the mining plan called for a gradual excavation into the hill from about 200 feet below this point. As mining proceeded over the next four years, several pegmatites were followed directly to their contact with the Buckner pegmatite. In 2009 we intersected the Buckner pegmatite and found numerous associated pegmatites. Interestingly, as we drew to within a few feet of the Buckner pegmatite we also encountered pockets that appeared to have no pegmatite association. These miarolitc cavities were formed by fluids and gases migrating from the Buckner pegmatite through the host granite until they pooled and bubbled out into small pockets.



Following pegs upward toward the Buckner "feeder" peg from about 150 feet downslope.	Evidence of the Buckner pegmatite could be seen on the surface due to the red color.	Work to unbury the pegmatite took over a week in 2009.


Buckner pegmatite is visible near large rock and angles downward.	Unburying working face a week later.	Face and Buckner peg are almost exposed.

GO TO PAGE TWO OF BUCKNER PEGMATITE

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As the pluton rises and crystallizes, fractures occur to accomodate the deformation.

Vertical and horizontal fractures occur.

Later stage magmatic fluids fill the fractures, crystallizing into pegmatites. Often vertical pegmaties are not noticeable.

Illustrations are by Joseph Dorris, please credit if you use any.