Our December 8th field trip to Dobell Ranch began with a chilly morning meet at Silver Saddle Rd. A scant, lucky, seven members ready to scout the open pits and grounds strewn with multi-colored Arizona Petrified Wood.
Our host, Rhonda Dobell and grandchildren, helped by pointing out some of the better material. It was as if we were shopping in a candy store with so many potential specimens to choose from, you ended up having to be very selective as to what you were bringing home. I think we all found what we wanted and then some. We all would like to have the tree trunks decorating our yards, but decided to be reasonable!
Lunch was prepared for all of us and we had fun with the younger grandkids. Then, when everyone was leaving, there were hugs for all around from the kids.
A very successful field trip that I’m sure we will make a repeat visit to, early next year.
Tales of the discovery and loss of rich gold mines such as The Lost Dutchman in the Superstition Mountains of Arizona and the El Naranjal lost gold mine in the Sierra Mountains of Mexico, as popularized by folklorist, J. Frank Dobie, in “Apache Gold and Yaqui Silver” have fascinated many of us. An extensive list of both lost gold and silver mines of the Southwest , each with extensive and entertaining descriptions of their histories, can be found in “Lost Treasure Tales” on the GeoZone Site [Ref 1].
Perhaps the lost mine tale that most of us are aware of, is that of the Lost Dutchman Mine [Ref 2]. One, of 62, hand drawn maps of its supposed location, made available in Reference 3, is shown in Figure 1 and orients it with respect to the prominent geological landmark, Weavers Needle, shown in Figure 2.
Two roots for the of name of the lost El Naranjal Mine have been attributed to its location near a grove of trees with oranges (naranjas) or to the orange color of the gold in its ore [Ref 3]. It is supposedly located at the bottom of canyon (Barranca) beside a river and near an abandoned hacienda.
Among many of the discussions about this mine, Treasurenet suggests that proof of the its existence lies in an old road sign naming the road to the mine in Sinaloa and in records found in Guadalajara, which were found by a British consul, describing production in the millions in the 17thCentury[Ref 4]. In another posting,
TreasureNet, [Ref 5], suggests its location fits that of an 1800’s lost, and very rich gold mine, in the region of the lost Tayopa silver mine [Ref 6], and in another post [Ref 7] that its location lies in the state of Durango.
November’s club field trip saw 10 members drive out to Arizona’sfamousMeteor Crater participating in a guided tour lasting about an hour.here is a brief description of the Craters history copied fromWikipediafor those that have not visited the Crater.
The crater was created about 50,000 years ago during the Pleistocene epoch when the local climate on the Colorado Plateau was much cooler and damper. The area was an open grassland dotted with woodlands inhabited by woolly mammoths and giant ground sloths.
The object that excavated the crater was a nickel-ironmeteorite about 50 meters, (160feet), across. The speed of the impact has been a subject of some debate. Modeling initially suggested that the meteorite struck at up to 20 kilometers per second, (12 miles per second), but more recent research suggests the impact was substantially slower, at 12.8 kilometers per second, (8.0 miles per second). It is believed that about half of the impactor’s bulk was vaporized during its descent through the atmosphere.
Having greatly enjoyed researching and writing about ancient and recent jewelry in my blog on Garnets (Glorious Garnets) and on silver jewelry in Silver II, I decided to present in this blog, “A Gallery of Ancient Gold Jewelry”, gold coinage and art works from around the world. Despite gold’s tendency to tarnish – its metallic beauty and its workability, stemming from its Mohs softness of 2.5-3, [Ref 1] it has long been a favorite with artisans using techniques such as casting of three-dimensional objects [Ref 2], chasing and repousse’, for the shaping of sheet gold, [Ref 3] and its alloys [Ref 4], and the forming of shapes using filagree and decorating with granulation [Ref 5], as well as the embossing coinage [Ref 6], and as an inlay [Ref 7]. Alloys of gold span the color spectrum offering a palette of colors to the artisan, ranging from purple to red, as well as white. Gold objects fabricated using these techniques comprise this gallery.
September’s field trip was well attended and productive, eight club members departed from the Market at Silver Saddle and State Route 89 for Gray Mountain. Upon our arrival to the area, Andrea Eubanks led the way to our primary collecting site, winding through geologic sandstone formations to a plateau above the Little Colorado River . There we fanned out across a wide area finding broken pieces of Petrified Wood left behind by a massive flood eon’s ago. Our recent rains helped uncover some cut-able prizes.
Members present, included Andrea, Gordon, Alan, Loewn, John & Beth and Marty & Linda.
This is the first of two Blogs on native gold. In the first I introduce the mineral and its properties, including a gallery of specimens exhibiting the crystal forms of gold and the effects of deposition conditions on forms of gold. Having just found out about it, I’ll also describe the deposition of gold by bacteria in alluvial deposits placers. In the following blog, I’ll present examples of ancient gold jewelry and art works from various locations around the world which demonstrate the innovative artisanship of early goldsmiths.
Among the native elements, Gold [Ref 1] because of its beautiful golden color, its rarity, and its aura of wealth and power, is a favorite among collectors and museum-goers [Ref 2][Ref 3][Ref 4]. Specimens of electrum, the lighter colored of alloy of gold, containing silver, [Ref 2]are also favorites. Specimens of both native gold and electrum from around the world occur in a variety of aesthetic and interesting forms ranging from single crystals and their groupings (Figs 5-9), twinned crystals (Figures 10-14), intricate dendrites, which are fern-like single crystals (Figures 14-15), and in spectacular sheet forms (Figure 16).
With a Mohs hardness in the range 2.5-3 gold is malleable which makes it easy to work into decorative forms by a goldsmiths. It also doesn’t oxidize, which facilitates melting it for casting, and soldering. In thick form, gold exhibits a rich yellow color due to its high reflectance of light in the yellow-red spectral range. In sufficiently thin form, as gold leaf, it transmits blue and green light. Its high specific gravity measures in the range 15-19.3 grams/(cubic centimeter), which allows efficient recovery of gold in placer deposits such as gold panning.
Gold, (and Electrum), crystallize in the isometric crystal system in it’s typical forms, shown in Figures 1-2. Gold forms twinned crystals about an octahedral plane as shown inFigures 3-5 [Ref 5 ]. Dendritic crystals result from repeated Spinel-twinning in a branched structure with branches at 60 degrees relative to each other. A native gold specimen referred to as wire gold, is not a wire in the sense of the native silver wire, (See the Native Silver Blog), but is an extended single group of multiple Spinel-Twinned crystals as shown in the specimens of Figures 12-13. Gold deposited in fractures with the host mineral, when exposed, possesses leaf-like forms as in Figure 15.
The Spinel-Twin is formed by a rotation of the lattices of each of the two crystals about an axis perpendicular to the octahedral plane, as demonstrated by the model of an octahedral crystal in Figures 4-5 [Ref 5].
Gallery of Native Gold Specimens
In many gold specimens the crystals do not display the perfection of form typical of some other minerals such as pyrite, but are skeletal with depressions, or [Ref 6], are also referred to as being hoppered [Ref 7]. Gold crystals can also exhibit interesting, complex twinned and dendritic forms. These departures from ideal forms stem from conditions of rapid deposition in absence of thermodynamic equilibrium [Ref 8]. Gold specimens featuring octahedral, cubic, wire, dendritic. and leaf forms, the latter, which in many instances is formed in interstices in fractured quartz [Ref 9].
Deposition of Gold By Bacteria
In searching the web, I found recent studies which, surprisingly to me, demonstrated the deposition of particulate gold by the action of specialized bacteria in alluvial deposits [Ref 10][Ref 11]. In the studies, the presence of toxic gold complexes was shown to initiate the formation of a population of bacteria which excretes enzymes that catalyze the formation of nanoparticles of gold, [Ref 12]. Aggregation of nanoparticles of silver and gold have been shown to participate in crystallization of these metals, which allow growth of gold on a nugget [Ref 13]. Bacteria resident in a biofilm [Ref 12], on the surface of a gold nugget could function as a source of gold which forms a gold coat on the crystal with sustained activity of the bacteria. A scanning electron microscope image of the bacteria in the biofilm on a gold nugget is shown in Figure16. The deposition process takes place for years to decades in order to accrue on a gold grain, suggesting that if the process can be speeded up, bacterial deposition could improve ore-processing [Ref 14].
This gallery of beautiful silver jewelry, coinage, and art works presents works from around the world, and spanning the ages from the 26th Dynasty of Egypt (664-525 BC) to the Art Deco Era (1909-1941 AD) [Ref 1, 2]. Works have been chosen to demonstrate the artisan’s methods of forming shapes in silver [Ref 3] by casting, engraving, repousse’, embossing, and using silver inlay to adorn other metal objects [Ref 4]
This is the first of two Blogs on native silver. In the first I will introduce the mineral, including a gallery of specimens, and in the following blog, “Ancient Silver Jewelry” I’ll present examples of ancient silver jewelry, coinage, and art works, which demonstrate the innovative artisanship of early silversmiths from varied locations around the world.
Among the native elements, silver, [Ref 1], is a favorite among mineral collectors, as it is for me. Silver offers variations in color from metallic silver-white to the optical interference colors of a thin coating film, (such as on copper sulfide minerals – see my earlier Copper Blog), to the sooty black of a thick coating. From locations around the world it occurs in a number of aesthetic and geometrically interesting forms, ranging from groupings of single crystals (Figures 1-2), spectacular fern-like dendritic arrays of crystals (Figures 3 & 4), and striking wire and sheet forms (Figure 5 & 6). The relative arrangement of crystals in, and the shape of, the dendrites has been found to depend on the conditions of the surrounding silver-bearing solution during deposition of the silver, [Ref 2]. Specimens of wires attached to the silver sulfide acanthite, (Ag2S), grow on oxidation of the sulfide mineral, which liberates the silver, as described below, both by roasting, [Ref 3], or by chemical reactions in solutions within both the oxidized and replacement zones of an ore body, (Slide 9 of [Ref 4]). The wires grow at the interface between the acanthite and silver by continuing the face centered cubic lattice shared by both the acanthite and the silver, [Ref 1]. The sulfur of the acanthite occupies the interstices between the silver atoms. X-Ray diffraction and microscopy have demonstrated the crystallinity of a native silver wire.
In order to share with you these beautiful and intriguing forms of native silver, I’ve included a comprehensive gallery of these forms from around the world, (Figures 3-17). I’ve also taken the liberty of including a favorite specimen from my silver collection in the gallery, (Figure 10).
Because the lore of lost precious metal mines, particularly those in Arizona, New Mexico, and Nevada fascinate many of us; I’ll begin referencing descriptions and histories of these mines and provide brief excerpts from the references. In this blog, the emphasis will be on lost silver mines and in future blogs on silver minerals. Future blogs on Gold and Gold minerals will also include lore & history of lost Gold mines.
Silver Crystal Forms
Silver belongs to the isometric crystal system, [Ref 1], and crystallizes in cubic and octahedral forms as shown in Figures 1 and 2. The forms reflect the symmetry of the isometric crystal system. Silver crystals form twins on the octahedral surfaces of two crystals resulting in a Spinel-Twin, [Ref 6], with the remainders of each of the octahedrons visible, as seen in Figure 3.
GALLERY OF NATIVE SILVER SPECIMENS
LOST SILVER MINES
The location of the Lost Duppa Silver Mine in Arizona, [Ref 8], lies in the numerous mines and ore deposits of the heavily mineralized Bradshaw Mountains, (Figures 11-16). When discovered, the deposit was a ledge of silver-bearing quartz located in one of the many steep canyons located on the east side, of the northern Bradshaw Mountains. The ore was native silver. After his initial find, Duppa failed to relocate his original path to the deposit and never found it again.
The Lost Silver Lode of Carbonate Creek, New Mexico, [Ref 11]
The discovery of lode was in the Kingston Mining District, located in the southern region of the Black Range in Southwestern New Mexico. Located within the range are the Chloride, Kingston, and Hermosa Silver Distracts which have been rich producers of the metal. The lost lode lies in the Kingston Silver Mining District shown in [Ref 12], which eventually produced silver amounting to over Six Million in USD. The lost lode was discovered along Carbonate Creek near the town of Kingston as surface float of acanthite (silver sulfide). The weights of pieces of the float ranged up to 250 pounds. Ultimately float yielding over 80,000 ounces was found, but the source of the float was never discovered.