Sandstone halide
Springdale / wood-hosted Ag-Cu-U-V
Metals on this play: ag, cu, u, v
Calibration
Silver Reef, Washington County, UT — Buckeye / White / Butte / East reefs. ~7 Moz Ag. Biek & Rohrer 2006; UGS GeoSights 37.253, -113.367.
The trap
Host. Fluvial sandstone (Springdale Member of Moenave; similar channel ss) with intraformational conglomerate and plant trash.
Trap. Chlorargyrite / chalcocite on carbonized or petrified plant remains. Metals leached from tuffaceous Chinle, trapped on organic reductant in porous ss on an anticline.
What a hit looks like. Bleached or iron-stained sandstone with carbon trash. Horn silver is invisible until you XRF the wood, not the pretty outcrop. Green Cu stain on logs is a gift. Yellow U bloom is a cousin, not a miss.
Wrong mountain
Do not XRF a Combined Metals limestone or a tungsten vein with this checklist. Do not chase pretty petrified wood inside a national park.
- Host is limestone or quartzite vein — that is Play E or F.
- Epithermal quartz-calcite in volcanics / granite — Play I (Eldorado / Keyhole).
- No carbon, no wood, no plant hash in the bed you are standing on.
- No Chinle-family source upsection or adjacent.
- NPS interior (Zion, Capitol Reef core) — access-killed, still mapped so you see why.
How to use the score
The score orders the day. It is a walk sort. It is not an assay, a mining claim, or permission to enter. Killed ground stays on the map so the boundary is visible. Private land, tribal land, and park interiors stay off the walk.