Some of my students have asked about the origin of the giant
gypsum crystals of Naica, and the type of mineral deposit Naica is. I asked
Pete Dilles, and he tells me “Naica is a classic carbonate replacement Pb-Zn-Ag
deposit; however it is more of a chimney morphology than manto like in form".
Still I believe the giant gypsum after anhydrite crystals are in manto caves.
Many of the world class carbonate-replacement deposits reside in Mexico with
its thick Mesozoic carbonate reefs. The
manto bodies often, but not always, follow paleo-karst (caves) which were
essentially cavities before being flooded with hydrothermal solutions. Age of mineralization
is Oligocene I believe.” Who am I to add to this, but seeing the
galena-sphalerite mineralization, the burrito-shape of some of the ore bodies
(plus chimneys as described by Pete), and the druse-like morphology of the
giant crystals I would suggest a mesothermal, Mississippi Valley type of
setting, where basinal fluids (perhaps connate waters) get hot as they
circulate in the lower reaches of thick sedimentary sequences, pick-up metals
and dissolved ions as they travel, and then precipitate their loads as they are
forced by hydraulic pressure up the sides of the basin. The giant crystals are
not accompanied by sulfides, so they might have formed by a different pulse of
hot connate water.
Today we are heading north, half way to the Mexico-US
border, to visit the archaeologic site of Paquimé, adjacent to the town of
Nuevo Casas Grandes. We have teamed with another of Raúl’s ubiquitous friends,
Maruisa, who is a professor at the university in the Department of Ecology and
Environment. Marusia is a chemical engineer by training, and by quite an
amazing coincidence worked in the same uranium prospect I studied for my MSc,
San Marcos, to investigate the extent to which radioactive uranium compounds had
dispersed into surface waters and soils. This brought her into the realm of
hydrogeology, and like happened with many of us got trapped by its interesting
complexity. Marusia has built herself a beautiful villa near the university,
which is where we picked her up early in the morning.
We left around 8 am, with myself at the wheel and Raúl on
the phone, contacting yet another friend, Blanca, who he has in Nuevo Casas
Grandes. He and his employees lived in Nuevo Casas Grandes 20 years ago, to
conduct a survey of the municipal water distribution network, and Blanca helped
him find a house large enough to accommodate them for several months. Finally
he put down the phone, all smiles, and told us that all was arranged: Blanca
would guide us through Paquimé, and her son Dino would prepare us a sushi banquet!
Sushi? In the desert, 500 km away from the nearest coast? Faith sure moves in
mysterious ways.
Paquimé is a “typical” Aridoamerican site, contemporary with
the Mogollón-Anasazi cultures of Arizona and New Mexico. In fact, to judge from
the style of pottery I would think they were the farthest outpost of the desert
cultures to the north, and probably the point of contact with the Mesoamerican
cultures to the south. http://inahchihuahua.gob.mx/sections.pl?id=43
The site that one visits was likely the ceremonial center,
which sits on a dry upland right at the edge of the flood plain of the Rio
Casas Grandes, and which was surrounded by a very dispersed population that
made the best possible use of the fertile flood plain. On the ceremonial center
they built their distinctive Casas Grandes or Big Houses, which
archaeologists believe were up to four stories high, built in the style of the
Pueblo Nations, by stacking one room over the other. The clusters were either
artisan guilds (for example the guild of the macaw feather providers), or
political or religious cores. It was a socially stratified society, with engineers,
as usual, solidly in the middle of the hierarchy. The engineers used some stone
to build low pyramids, or to line the complex hydraulic system that served to
store and deliver water to the tall houses.
Construction was based on adobe mud (but not adobe bricks),
which was apparently formed using wood forms that were filled with mud and then
removed once the mud had set (wood was kind of scarce). That they managed to
build four-stories houses this way is pretty amazing! This type of construction
is, unfortunately, easily weathered and eroded by the rare but powerful desert
rains, so the site must have decayed into a big mound of rubble until
archaeological restoration started in the late 1930’s. Today it looks like a
giant hamster maze, with low consolidated walls, maybe half a meter wide, that
give the visitor but a pale idea of the bustling metropolis this desert town
might had been ca. 1200 AD.
Unfortunately the museum of the site was closed, but asking
for permission to go to the bathroom I was able to glimpse beautiful pottery of
the type so well known to visitors to the Pueblos of New Mexico.
Dinner time came at last, and as we drove to the wide by
sunbaked streets of Nuevo Casas Grandes I had to question, once again, the
wisdom of having sushi for dinner.
Side note: The folks from Chihuahua have a
very funny way of pronouncing the “ch”, which comes more as a “sh” when spoken
(e.g., Shihuahua for Chihuahua or mushasha for muchacha). They make an
exception for the word sushi, which they pronounce “suchi” with a hard “ch” sound,
similar to the word fuchi!
Anyway, a few meters down a dusty road to find the bombastic
“Nuevo Casas Grandes Sushi and Seafood Bar”, where our host, Dino (like in the
dog of the Flintstones), welcomes Raúl as his long-lost uncle, attired in
something that looked like a cowboy wearing a Japanese head band. He then
ushered us into one of the tables, and right away welcomed us with a mountain
of spicy tuna cucumber salad, “as an appetizer” and a yummy promise of future
dishes. It was absolutely delicious, delicately spiced to perfection, and I
would have been glad if that had been the extent of the meal. But no, out
followed a collection of his most delicious rolls, all named after local people
and landmarks, including the avocado Dino roll, and the crunchy Paquimé roll.
Heavenly. Finally we got a big platter of the lightest vegetable and shrimp
tempura I have ever tasted. I kid you not, this is one of the best “suchi”
meals I have had, and I hereby proclaim Dino as one of the great chefs of the
art. Turns out that he has run his restaurant for over 20 years (so he got to
feed Raúl and his associates during the months they spent here), adding a few
cooked seafood dishes for the stubborn Mexican taste.
For the grand finale Blanca took us to a town whose name I
don’t remember, where museum quality pottery has been produced for nearly 50
years. The pieces are exquisite, again inspired in the Pueblo style, and would
be perfect for a house decorated in “desert style”. Now wait, we had Marusia with
us, who has a gorgeous house that could use a few of these fabulous pieces of
art. So she was an active shopper with a keen eye, and was ready to take the
plunge when I held her back and told her “I suspect the prices are in dollars”,
which they were, and that put an end to her urge to buy the shop.
We had a fabulous day, although we spent 3 hours
getting there and 3 hours getting back. We shared the drive, and Raúl was very
good surrendering his cell phone for the middle stretch, so we all traveled in
peace and friendly conversation. When it was my turn to drive the last leg, Marusia
offered him the shotgun seat, but he thirstily declined, and pounced on his
beloved cell phone. From there on we didn’t hear a peep from him back there.
