A Passion For Gold: An Autobiography

1. Geology 101: Nevada Gold and Mountain Building

Chapter 1 Geology 101 nevada gold and mountain building “The time has come,” the Walrus said, “To talk of many things, of shoes and ships and sealing wax, and of cabbages and kings.” —lewis carroll, Alice’s Adventures in Wonderland Gold, the metal of exquisite beauty, has intrigued ancient and modern man alike. If ancient man found crystals of gold, probably in quartz veins that are sometimes exposed in mineralized areas, he might have fashioned primitive jewelry by stringing the crystals on a thong cut from a skin of some animal he had killed and eaten. So adorned, he would have been the envy of his tribe. Now we find gold crystals in mines dug deep into the earth, and they are as prized today as they were in ancient times. The ore is also found as nuggets of placer gold in streams. In 1849 in California and in 1898 in Alaska and the Canadian Yukon, prospectors were excited by discoveries of placer gold. Gold is uniquely malleable and has long been the metal of choice for fashioning art objects; it can be carved, cast, or beaten into tissuethin sheets. In 1539 Benvenuto Cellini of Florence, Italy, began to fashion a gold saltcellar for King Francis I of France. This magnificent work was finished in 1543 and is now displayed in the Vienna Art Museum (Wienkunst Museum). I can easily understand Cellini’s dou- Fig. 1.1. Leaf gold with trigons found in the Wadley Mine, Willow Creek Canyon, Pershing County, Nevada. Courtesy of Lois Calder Baum. Fig. 1.2. Cellini saltcellar. Courtesy of the Vienna Art Museum, Austria. ble passion—for gold and for the art made from it. Most comparable works of that period have been melted down, and their artistic value has been destroyed. What a pity! Gold is found in many geologic environments, as lodes (such as quartz veins found in both cold and hot environments), as bodies that replace (substitute for) favorable beds such as limestone, and as sedimentary placer deposits in stream gravel. The geologic processes that form gold deposits include release of gold from deep in the crust and mantle of the earth, and transportation of it upward, to spots nearer the surface. This can be a slow process, but geologic time is long; there is plenty of time for everything. We will consider events that go back far into Precambrian time, i.e., more than 550 million years ago, as well as events that took place within modern history. A geologic time scale divides geologic history into periods. These periods by and large record events such as sedimentation of related rocks or similar mountain-building events. Hang on tight, we’re going on a wild ride! Even now, at the age of ninety-one and of relatively sound body and mind, I find that geology continues to be a major element in my life. Though I can no longer tackle the rugged mountains of the West, I will continue to study, write, and talk about mountain building and related ore deposits. The western cordillera, or mountains of the western United States, has been my laboratory. The complex processes that formed these mountain ranges over the last 300 million years reveal an earth in slow but constant motion with many geological events occurring together. If we could compress time, the enormity of these changes would overwhelm even the most seasoned geologist. Orogeny, the geological term for mountain building, has always interested scientists, who early on devised a contraction theory based on a shrinking earth; they compared mountains to wrinkles as on a drying orange. Early geologists knew that the earth was originally molten, and they suggested that as it cooled, it shrank, forming mountains. But had this been the case, mountains would have formed in belts of about the same age. The record showed that mountains had formed at many different times during the earth’s long history , so the theory was discarded. Nevada Gold and Mountain Building 3 Fig. 1.3. Geologic time scale. Much later, geologists began to note that mountains formed mainly on the margins of continents and in subsiding troughs. This concept was called the geosynclinal theory of orogeny. All the great mountain ranges, including the Appalachians and Rockies, formed in basins or troughs, but something was lacking—mountain ranges were generally folded and...