Tuesday, March 28, 2017

Tales of the Mojave: A Dry Placer

And now, let us continue with my Tales of the Mojave series. In our last post, we had barely left town—town being Reno, NV, hundreds of miles to the north, and we being Allie and I, two young and fairly junior geologists: I was beginning my fourth full year as an exploration geologist; Allie was beginning her first. Besides the several recon targets I had generated while we were still in Reno, we also had a placer submittal to examine and evaluate.

A Dime a Dozen


Placer claims are a dime a dozen in the Mojave, and they are typically worthless—at least in my limited experience. (Actual placer miners might disagree with my assessment, but I'm using the mindset of large, hard-rock mining and exploration companies.) Unlike lode mining claims, placer claims can be increased in size if an association (group of more than one person) locates the claim: The usual 20 acres per lode claim or individual placer claim can be as large as 160 acres in an association placer when located by 8 or more claimants.[1] Association placers can, in other words, cover an entire quarter section, making it possible to cover a lot of ground with relatively few claims, something that was done widely across the lowlands of the Mojave Desert of California in the 1980s (and elsewhere, like Arizona, and elsewhen, perhaps even right now). Many of the placer submittals we received during the 80s were located not only for gold, but also for platinum, an element that is quite rare in the placer settings of the southwestern deserts.
“A degree of skepticism should also be reserved for ores said to contain uncommon metals or minerals. Because of their rarity, these substances may command a very high price and are therefore extremely attractive to the investor. The platinum-group metals including platinum, palladium, rhodium, ruthenium, iridium, and osmium, are the darlings of the swindler. Considering their high unit-value, even minute amounts of these metals appear to be a reasonably good bet to the innocent investor.”
–from Mining Scams, AZGS
In any case, I’m not sure why we were called upon to appraise these particular placer claims, nor do I remember their exact location or size.[2] I did already know a few things about placer deposits—a little—having looked at a number of placer submittals in the California foothills earlier that year. The Mojave placer, however, was different from those in the Mother Lode region of California, being “a dry placer” or “desert placer,” which means they were not located on or very close to any actively running water. Flash floods in usually dry washes, and sheet runoff across the fans during storms had formed the sand and gravel deposits that might (or might not) contain placer gold, but the nearest naturally running water was several miles to the southeast in the Colorado River. (Water in the nearby Colorado River Aqueduct was nearer by half, but was inaccessible to any would-be placer operators, including us.[3])

The Desert Sun


The desert sun glared through the windshield of the truck as if to threaten us with heat stroke or worse, and heat waves rose inexorably from broad alluvial fans and bajadas, countless meandering dry washes, and endless desert pavement. As we turned onto dirt somewhere between Vidal Junction, CA, and Parker, AZ, I wondered what we were getting ourselves into. It wasn’t just the question of evaluating a dry placer property located miles from running water, but also the larger question: What were we doing in the Mojave in June? We drove down the fan, over rocks and by countless jumping cholla, not knowing for sure where we'd end up, not having to meet with the prospector, as one does so often when checking out a submittal. It didn't take long, really, before we found the spot, nearly lost in low, decapitated hills and erratic dry washes south of the Whipple Mountains, buried under  a millennium’s worth of accumulated sand and dust. Dust covers entire mountain ranges in the western Mojave Desert, and it collects on pool tables in towns up and down the Colorado River in the eastern Mojave. Parker, Arizona, is one of those towns. Hopefully we'll stop in Parker some other time.
We had brought extra water with us in 5-gallon containers, including 1 or 2 basic upright cooler types and several clear, collapsible plastic types. The extra water was, at this point, for evaluation of the claims, not for our own hydration, but the extra containers would serve us well as our expedition unfolded. So far we hadn't noticed anything untoward in the flavor of the water, primarily because we had filled our containers north of the NV-CA line, probably in Reno. Desert water can taste absolutely awful.

As property reviewers, we would not only have to determine whether gold was present, but we would have to make some deliberation as to the feasibility of mining by a fairly sizable company. I could think of three scenarios for processing (mining) any placer deposit we found:[4] 1) haul water into the area from the Colorado River or from Lake Havasu to wet-separate the heavy gold from the lighter quartz and feldspar sand and gravel, 2) haul the gold-bearing sand and gravel to the water, presumably the Colorado River, for wet-separation offsite (no doubt requiring further land acquisition), or 3) dry wash the sand and gravels without water. Dry washing using the oldtimers' dry winnowing method is notoriously inefficient at gold recovery and can be totally worthless if not done with extreme care and diligence.
How we get gold in California: winnowing gold, near Chinese camp.
Original in Harper's Monthly, v. 20, 1860; source: Library of Congress (no known restrictions).
Of course there are more current methods of dry washing available than winnowing, if you happen to have some gold-bearing sands and gravels on your Mojave placer claims. I'd look into the Bedrock Dreams website, which shows many possibilities and has a lot of info for the up-and-coming small-time gold miner (hard rock and placer).

The Dry Wash


At the dry wash, we camped in trenches dug by the claim holder. In the “cool” of the evening—when temperatures dropped somewhere between 70º and 85ºF by morning—we panned for gold using the precious water we had hauled in. Because the paved roads of Highways 95 and 62 and the desert-river town of Parker were not so far away, we went ahead and used a lot of our water for panning. We didn't have to save most of the water for drinking, which we would have done had we been camping four hours away—over hot, dusty roads—from anywhere of desert significance: any place with water, food, people, and, preferably, gas, spare parts, and tires (the latter preferences ruled out places like Goffs and Essex)

We were lucky, and our pans showed some color: a few, small flecks of gold almost too tiny to see. With repeated tries, we consistently got 2 to 4 colors in each pan. After we used up our extra water, which happened faster than we had envisioned, we took to dry panning. (It doesn't matter how close you are to town; it's ill-advised to use up all your water. You might need it during some unexpected, unplanned-for vehicle mishap or environmental disaster like a clogged fuel filter, a flat, a washed-out road, or a flash flood. See A Few Rules of the Desert.)

At some point, perhaps out of boredom, we gave up on classic dry panning, which looks a lot like regular panning but with tons of dust. One more time we filled the gold pan with the weakly gold-bearing alluvial sand and threw the material expectantly skyward. The evening breeze blew the lightweight fines toward Arizona—where all Mojave sand and dust aspires to reach—and the heavier material fell back toward the pan. We had reinvented dry winnowing! In theory, we should, after several skyward tosses of material, have been left with a few heavies, some black sand, and a few flecks of gold. We weren't, though; maybe our technique was subpar. Regular wet-wash gold panning requires some skill, but if there’s gold in the pan, even an unskilled person will usually find it—although I've seen newbies mistake golden-colored quartz, gold-flecked biotite, and that common mineral pyrite, AKA fool’s gold, for gold. All of these minerals might fool some of the people some of the time, though with practice or a good course in mineralogy, you should not get duped by any of them. Gold is the only mineral that will shine or look bright golden yellow in the shade. Pyrite pales next to gold, and put in the shade it won’t shine—it becomes just another mineral, barely tinted beyond pale brown, nowhere near the bright golden yellow of real gold. (The exact color of gold depends on its fineness and upon which of several other elements, notably Ag, Cu, Fe, Pt, Cd, might be contained within the gold. These factors will affect how bright yellow or golden the gold looks. And then there's chalcopyrite, not as common as pyrite, but often lying somewhere between pyrite and gold in it's yellow-gold sheen. So it is possible to be fooled. But don't be. A Niton™XL3t GOLDD+ xrf analyzer can be a friend.)

Dry panning and air winnowing hadn't done much besides create a lot of dust and two ravenous geologists. So we put the gold pans away and turned our thoughts toward dinner. The sun was fairly low over the Turtle Mountains to the northwest, and my time estimation method indicated we had about 1.5 hours to sunset. What should we eat? We went ahead and established our Mojave Desert, south-of-the-border-style cuisine of tacos or burritos, with avocado and as much hot salsa and jalapeño as we could stand. This type of food is not too heavy for the heat, and (I’ll swear to this—or ask any desert rat) the spicy burning of the peppers created a cooling effect, something we would really need as our time in the desert progressed. Besides, there’s enough vitamin C in the peppers to fight scurvy, a credible desert plague: Rapid melting of the ice will spoil many vegetables and a few fruits over the course of our stay.

Yeah, we had just arrived in the desert and were still greenhorns, not quite able to call ourselves Mojave Desert rats. Not yet.
A little fooling around with SunCalc produced this reproduction of sunrise and sunset at our campsite (approximate location and date).
As the sun sank behind the Mopah Peaks, I thought about the next day. We'd be moving upslope into the Whipple Mountains proper. We were done with the placer submittal and, back in Reno, would recommend “No Further Work.” Although we didn't really know how large the weakly gold-bearing sands are, we suspecedt that their likely flash-flood origin from upstream copper-gold diggings in the Whipples would make mapping out the gold bars and channels difficult at best.

To be continued...

Notes:


[1] (Read about basic claim location rules here.)

[2] In later years, when working for Former Mining Company, I rarely took on placer submittals; in fact I actively avoided them, especially after one particular submittal (a classic scam) led to a fabricated conflict between our lode claims and the association placer claims of the submitters.

[3] The Colorado River Aqueduct is a 242-mi (392 km) water conveyance in southern California. The aqueduct diverts water from the Colorado River at Lake Havasu (at Parker Dam north of Parker, AZ) on the California-Arizona border west across the Mojave Desert to the east side of the Santa Ana Mountains. The aqueduct is operated by the Metropolitan Water District of Southern California (MWD) as one of the primary sources of drinking water in southern California.

[4] A note about my usage of "found" and "deposit." We knew there were claims for placer gold. We didn't know for sure if any gold existed on the property or in the area. If there was gold in the dry washes, the claim owner had discovered it, not us. We, however, wouldn't think of any gold on the claims as an economic deposit until it had been tested, which usually involves drilling or—especially in the case of placers—small-scale test mining. It's not considered accurate to call a mineral occurrence a deposit until it meets economic parameters and passes mining feasibility studies. It is therefore correct for me to assert that the claim owner discovered the gold, but Northern Mining Company's representatives (us!) might discover a gold deposit.

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