Tag Archives: copper

New Copperopolis? Goldsborough? Silverberg…?

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In 1927, at the apex of Hollywood’s Art-Deco silent movie Golden Age, sleepy Lankershim was upgraded to “North Hollywood.” And the Keystone Studios’ old keystone, Mack Sennett, led investors to buy the Laurelwood tract of the old Lankershim lands, adjacent to the newly-styled NoHo. Just where Laurel Canyon spills down the Hills onto the banks of the Mighty Los Angeles, he opened ‘Mack Sennett Studios.’ (Later, Republic; then MTM; now CBS.)

The dream factory was only the centerpiece of an entire planned community, the Valley’s first office-park/retail-strip/tract-home automobile suburb.Sennett chose his land well: this is one of the most temperate, healthful, convenient, and visually expansive bits of real estate in California.

Sennett gave his sylvan glens and lush riverbank house-lots a jazzy name that was catnip for Hollywood’s cultural-creative yuppies: ‘Studio City.” Dusty old Camino Real got its kick-line of Baja fan palms; Ventura Blvd. remains one of LA’s swankiest and most iconic strips.

The point is it’s a bizarre place to find a copper porphyry! (Don’t roll your eyes, P.R., you knew geology was coming.)

But as we’ve seen, the Santa Monicas are exactly the sort of place to expect to find a copper porphyry. Rather, call them IOCG Deposits, as the investors’ brochures do (Iron oxide, copper, gold, that is).

The ridges and pound-cake hills of Laurel Crest along Mulholland Drive near the Overlooks, contain old magma tubes, breccia-filled feeder pipes, conglomerate columns and various other intrusive sills and dikes. This is plumbing that has developed over the past 15 million years: residual intrusive volcanics from the forces of collision and compression, thrust and subduction, rotation, folding, fracking, and cracking.

The brown breccia is dense, nicely concentrated chalcopyrite. The most dense, the most cupric copper ore, is probably located in the three or four feet below Mulholland Drive.

Old volcanic tubes, as well as faults, of which there are many here, can be siphons for deep hot acid brine. Deep hot acid brine when pushed up near the surface, into the cool meteoric groundwater cycling zone, creates thermal and chemical reactions that create dispersed, and over time concentrated, copper, lead, nickel, gold, etc. deposits. Molybdenum. Zinc. But here…copper.

  • Winter. Nothing remarkable about the hill, except for the Student Prince’s house on top.
  • January 27, 2021. Only glimmers of gray outcropping through yellow Monterey shales.
  • Six months later, the turf is poisoned, the chaparral helps outline the slope’s groundwater chemistry, and distinct lobed mouths of porphyries have emerged, ringing the poundcake hill.

It seems that just a few months ago the hills started — or certainly, restarted, after a dormancy — mineralizing. My guess is the July, 2020 Pacoima thrust-fault 4.4 earthquake forced opened fault valves, or closed others, or both. Something in the plumbing changed. When the rains came after that — especially a gully-washer rain in December — it may have stripped the topsoil cap, reducing slightly the sealing — ceiling — layer of turf. With a water table now high enough to draw the brines up to the rocky roadside ridges, and these awesome structures are revealed. Though it had been weeks since there was any rain, note the porphyry hill is still trickling rivulets of acidified water:

The Overlook here features conglomerate boulders found on-site. It’s easy to dismiss their markings as grafitti: gooey white or powdery gray, blue or teal, red, magenta, and black streaks on surfaces. They aren’t defacement: they are minerals, copper relatives: bornite, malachite, chrysocolla, azurite, cuprite, chalcite.

  • CHRYSOCOLLA
  • AZURITE
  • White goo is quartz; it can frequently be found as splashes and spatters over rocks
  • Or as a binder matrix holding heavy minerals.
  • Gang tags?
  • A menacing pirate, spray-painted on the boulder?
  • No, it’s the black crystals of CHALCOCITE, emerging in the familiar crown or star patterns.
  • AZURITE
  • CUPRITE, which can be scarlet or magenta.

The View will mention, but not dwell upon, the ironies and implications of porphyries appearing in the Hollywood Hills. The rich get richer; but to own their wealth they’d have to destroy their Paradise. Also, are there potential toxicities to the Los Angeles river which drains the Hills? Are there bad-air dangers to homeowners above, or motorists cruising Mulholland, or Overlook Viewers from sudden off-gassing events? Are these re-emergent processes just a quick residual one-off event, a last hurrah, a blip from the recent temblor? Or have homeowners just loaded their yards in the Hills with so much piped-in sprinkler water since 1915, that we’ve re-set the water table and kickstarted a new age of copper formation? Is Studio City yesterday’s movie colony, or tomorrow’s burnt-over strip-mining district? Watch this space, and see!

April Fools’ Gold

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The View is reeling these days from the fast-paced, hectic, thrill-a-minute, presto–chango world of local geology. I haven’t been blogging because I’m too busy learning from the rapidly changing land. I feel like the boy Wart, being given his lessons in Deep Time by old Merlin. Every time I set foot on a trail in this remarkable Valley, puzzled by its mysteries — suddenly, there, in this hillside, or that chasm, or lying at my feet, I find a stunning new revelation of whatever point of ignorance I’ve been working my brain around. Which then brings up a hundred new questions! I’ve broken a couple computers web-searching Chinese papers on “convergent accretion wedges.”

Mostly I’ve been baffled lately by “mineralization,” that strange alchemy that apparently creates lead, zinc, copper, silver, gold…and pyrite and molybdenum and arsenic and graphite and uranium and all the rest. It’s apparently a phreatic process that is dependent upon fine changes in the water table. Iron, sulfur, and carbon dissolved in water deep under the mountains periodically boils or bubbles or cold-seeps up through the rocks (or, sands, it turns out…remember gold nuggets in creek beds?). When the pressure drops or the temperature or acidity become too much for it, the water vapor trapped in the rocks goes pffft! up a long spout of the loosest conglomerates; and the metals and salts dissolved in the water precipitate out over or into the cracks of the surrounding rocks, where, if the type of country rock sitting there is right, makes more al-chemistry take place, creating more and more amazing minerals.

This process, I have been reading about but couldn’t comprehend in the slightest! Maybe you can’t either, to read that paragraph. But I found a demonstration on the surface, just a few hours after it happened, and I was so excited I must share it with Patient Reader. I won’t explain further, just bear in mind the above facts, and accept that geology is now and didn’t happen in the past. View on.

  • Trail on top of left ridge up Sugarloaf
  • This geologically wonderful Viewpoint — wonderful west
…wonderful east. Hallo, what’s that gleaming in the path?
  • Yes, a fools’ gilded dandelion. I may have missed the sulfur cloud by minutes. They can kill hikers!

I became instantly irate about the obvious prank vandalism of kids with spray-cans — loathing as I do the graffiti appearing on rocks EVERYWHERE these days, especially with the kids out of school during COVID. Trying to fool people…! But then again, it’s right where mineralization, I think, has been happening. What’s further up the path? How’s the griffone?

I had come there looking to see if the griffone was still there. Was it? Yes…
  • 9…side vents to mud volcanoes).
  • Wow —fresh coating of lacquery-coppery mineral wash!

The vent is the lower crack with the burnt twigs. To the left is murmuring sand from carbonated water or boiling steam. It blew the stream of fluid right under the extruding gneiss vein, which got washed and transformed by that coppery-green-gold finish, like the rocks on the ridge. Fluid is venting from the crease right where the trail meets the slope. The theory is, since the road cut interrupted the flow to the dome, the spot just in the crease of the road was the first place this highly pressured deep earth fluid found an opening to low surface air pressure, where it went poof! leaving the heavy minerals sprayed on the rock and sand — exactly like a kid with a spray can! In this case I’m pretty sure that what I found is chalcopyrite, the chief copper ore, and along with iron pyrite, one of the true “fools’ golds.”

  • The brassy coppery-greeny-gold of fresh pyrite!
  • Of course, the real fool finding fools’ gold, is the fool who, finding pyrite, sells his claim thinking it’s worthless. The savvy prospector buys it, for he knows pyrite and gold — and silver and copper — all take the same steam elevator. These pyritey rocks are also nicely cooked with traces of many rare metals deep inside.

For a guy who has been blundering around lately collecting mineralized ore samples to pound out and pan down looking for a few gold flakes…a process I DON’T EVER WANT TO REPEAT…

…I’ll take the fools’ gold, and the free lesson in Golden State geology, picked up off the trail side float. Gee whillikers, watch this space. Marvellous and strange things are happening in the Valley, and the View is on it!