"THE WOLF CREEK FORMATION"

A new construction site on the corner of Old Norcross Road and Satellite Blvd. (adjacent to the Gwinnett Place Mail) in Duluth, Georgia has exposed the contact zone between the Norcross Gneiss and the Wolf Creek Formation. The Geology of the Greater Atlanta Region (McConnell and Abrams, 1984) describes the Norcross Gneiss as a light gray epidote-biotite-muscovite plagiociase gneiss locally containing amphibolite, and the Wolf Creek Formation as thinly laminated, fine-grained amphibolite interlayered with lustrous, silvery-gray biotite-muscovite schist. Blasting and excavating at the construction site has exposed about thirty vertical feet of both rock units. The exposure is manifested as a gently folded synform/antiform complex generally trending S300E. Both rock units contain large quartz-feldspar-epidote porphyroblasts locally rich with sulfide mineralization (largely massive pyrite). A large (about 50 feet in diameter) roughly circular coarse-grained granite body was exposed within an amphibolite-rich area of the Wolf Creek Formation. The following is a list of mineral species found at this site:

* Hornblende - As single crystals, crystal aggregates and massive. Some nice micromounts of single crystals in small pegmatite lenses were collected.

* Acmite (Aegerine) - As acicular bladed, nicely terminated micro-crystals in small pegmatite lenses within amphibolite-rich schist in the Wolf Creek Formation.

* Actinolite - As interlocking micro crystal sprays of light green to greenish black actinolite within massive hornblende matrix. Found immediately adjacent to the granite body.

* Chlorite - As massive bright green micro-crystals in coarsely crystallized hornblende adjacent to the granite body and as green coatings in vugs with pyrite and possibly prehnite.

* Pyrite - As massive material and micro-crystal druses in hornblende vugs. Found in both rock units. Some world-class micromounts of pyrite crystals within hornblende matrix were collected from the site.

* Chalcopyrite - As massive material and well-defined micro-crystals in vugs in massive hornblende. Also present as cavity fillings in coarsely crystallized hornblende and augite. Some world-class micromounts of chalcopyrite were collected. Beautiful micro-crystals set in vugs in black hornblende with some of the chalcopyrite crystals tarnished a pretty metallic sky blue!

* Epidote - As massive light green material.

* Garnet (Almandine) - As deep peach colored micro-crystals in fine-grained quartz feldspar matrix in the chill zone of the granite body. Very pretty micromounts.

* Prehnite - This mineral species is pending positive identification by x-ray diffraction. If the I.D. holds it will be the first reported occurrence of this material in Gwinneft County. Occurs as small rounded translucent very light green to clear crystal aggregates in vugs in hornblende schist with pyrite, chalcopyrite, and chlorite. Very attractive world-class micromounts.

* Tourmaline - As both schorl and dravite. In quartz/feldspar veins adjacent to the granite body. Occurs admixed with hornblende, augite and actinolite. Very interesting micromounts of transparent dravite in quartz matrix were collected. Some attractive hand specimens of schorl crystal sprays were also collected.

* Augite - As black, blocky crystals and crystal aggregates. Usually admixed with hornblende and tourmaline. Found in quartz/feldspar veins in hornblende matrix adjacent to the granite body.


* Adularia - As transparent rhombohedral micro-crystals in small vuggy pegmatite lenses in amphibolite schist matrix.

* Quartz - As massive blebs and grains in amphibolite matrix. Also present as vein material. No crystals of quartz were found at the site.

* Feldspar - As both plagiociase and orthoclase. Large phenocrysts of both species in the granite body. Feldspar in the primary rock units is largely plagiociase. Most specimens exhibit polysynthetic twinning. Most of the plagiociase exhibits a cherry red fluorescence under short wave ultraviolet light.

The excavation at the construction site is almost complete so there is not much of the rock exposure remaining. However these same rock units crop out in other areas in the Atlanta Region. With all the construction going on in the area, there are other rock exposures to be investigated. Be sure to ask permission from the property owner prior to collecting. There is much mineralogy that can be documented from our own area.

---

Additional exploration work is being conducted on the exposure of the Wolf Creek Formation in the Gwinnett Mail area near Duluth, Georgia. Several new mineral finds have been located:

* Sulfur - Occurs as free pale lemon yellow micro crystals in vugs within iron stained quartzite. The sulfur crystals are associated with partially dissolved pyrite. In some cases the micro sulfur crystals are attached to the partially dissolved pyrite. Only one occurrence of the mineral has been found in this exposure of the Wolf Creek Formation.

* Calcite - Occurs as micro rhombohedral yellow to orange-yellow crystals as cavity and vug fillings in massive quartz veins implaced in amphibolite schist. Pyrite and chalcopyrite microcrystals are associated with the calcite.

* Thomsonite - Occurs as micro spherical crystal aggregates in pyrite vugs within massive quartz veins implaced in amphibolite schist.

* Red Zoisite with green Zoisite and Eqidote with QuartzTremolite - Occurs as white acicular to fibrous micro crystals. Only two small occurrences of this mineral have been found to date within the Wolf Creek exposure.

* Zoisite - Occurs as pale to dark red micro crystals and masses in epidote/quartz prophroblasts. In detail, the zoisite occurs in a series of vugs within a granular epidote matrix, which itself is within the prophroblast structure. Most of the red zoisite micro crystals are translucent with a few transparent gemmy micro crystals. Only one occurence of the zoisite has been found.

* Prehnite - As pale green bladed micro-crystals and pale gray micro crystal aggregates joined on the 1 0 0 plane forming barrel like structures. This mineral has been reported earlier from this same site, associated with sulphide mineralization. This new occurrence is associated with quartz, feldspar and schorl tourmaline in small solution cavities in the feldspar matrix.

NOTE: This exposure of the Wolf Creek Formation (the corner of Satellite Blvd. and Old Norcross Road in Gwinnett County) is now essentially closed to collectors. Active building is now in progress at the site. The site has been a prolific producer of mineral species. Of interest is mineral content in other exposures in the Wolf Creek Formation.

---

---