Rush, a Mining Ghost Town
Current Status: All but two mines are on Federal land and are closed to collectors. The Philadelphia mine sold; status unknown.
THE BEST KNOWN and most prolific specimen producing region of north Arkansas for many years was the Rush Creek zinc district of Marion County. There were 12 named underground mines in the district. Of these, most specimen material came from the Monte Cristo and Philadelphia mines. The district is best known for the specimens of yellow smithsonite, called turkey fat by the miners, produced when mining was active.
The Monte Cristo has been closed to public collecting since the property became part of the Buffalo National Park in 1972, but mineral collectors continued to access the old adit until it was closed with bat gates in 1996. Marvelous specimens of various colored smithsonite (yellow, golden, brown, reddish brown, gray, and even greenish) were the most desired (photo below), but many examples of different forms of secondary calcite, dolomite rhombs on druzy quartz, and primary brown sphalerite (second photo below) coated with oriented growths of chalcopyrite crystals were also collected. 
Micromounters looked for thin pockets in the walls which yielded scattered bow tie forms of yellow smithsonite on colorless drusy quartz. Even an occasional clean micro-sphalerite crystal was seen. Thick botryoidal fluorescent 
blue-white calcite coatings were mistaken by many collectors for smithsonite. An adjacent portal that opened into a large natural cave system produced stubby quartz crystals on chert matrix that sometimes contain included chalcopyrite. Some primary honey-colored rough calcite crystals were present in this area, along with scarce greenish aragonite needle coatings (colored by secondary malachite)photo below. The Monte Cristo was the last active mine in the district, having closed in 1962.
The other mine, privately owned, that produced many specimens was the Philadelphia. Present ownership is in question. In the early 1960's, a collector- dealer got permission to mine specimens and many spectacular yellow dolomite crystals on druzy quartz matrix were available for collectors. These specimens resulted from the partial replacement of the typical pink dolomite by tiny yellow smithsonite crystals. In the 1980's many specimens of smithsonite were recovered by collectors.
The backs of both adits reached into the unweathered zones of mineralization, a primary dolomite-coated chert breccia. In pockets in the breccia, fresh mineralization could be seen, but not so easily extracted. The rock was exceedingly hard. Many specimens were recovered from the floor rubble of both mines.
This was a famous collecting district known for many years by rockhounds. It, unfortunately, is now essentially closed. However, you may still come across specimens that can be purchased when fellow collectors decide to clean out their duplicates. At reasonable prices, I have purchased some really nice specimens from different individual collectors in the past few years. Because they collected them, they just don't seem to understand that there will not be anymore of these specimens available in the near future.
For further reading, I suggest:
Rush Creek Mining District, Marion County, Arkansas -- A Synoptic View by J. M . Howard, 1989, Rocks and Minerals, v. 64, no. 4, p. 284-92. The Arkansas Issue.