Description
The northern imbricate of the Copper Basin reverse fault is located west of Little Picacho Wash. At this site, the Quechan Volcanics occur in both the hanging and foot wall blocks, and the fault strikes EW and dips 52° S. Five samples from the fault core, 5 samples from the inner damage zone, and 4 samples from the least altered outer damage zone were collected from the hanging wall block and were analyzed for major element chemistry. Utilizing statistical tests provided in the software program, Assessing Element Immobility, revealed that Si, Fe, Al, and Mg are good candidates for an immobile reference frame. Using Si and Fe as the reference frame indicated that during development of the inner damage zone as much as 11– 15% of the P mass was lost. Though similar losses in phosphorous mass are indicated by an Al and Mg reference frame results are not statistically significant. In contrast to the inner damage zone, statistically significant increases of ~208% – ~256% Ca mass, ~143% – ~182% of LOI mass, and ~17% – ~35% of bulk mass are indicated by all 4 reference frame elements for the fault core. In addition, the reference frame Fe, Al, and Mg indicates an increase of ~13– 31% Ti mass. Even though a Reference frame of Fe and Al indicated that~13– ~18% of the mass of P was lost, a reference frame of Si and Mg indicates that such losses within the fault core are not statistically significant. In short, given that calcite is a prominent secondary mineral in the fault core, the above data indicate that the core was likely invaded by fluids supersaturated with Ca and CO2. In addition, to account for the increase in LOI mass, such fluids must have reacted with the comminuted silicate mineral framework to produce smectite + illite/smectite, the clay mineral assemblage identified by my colleague N. Seitz. Of some note, though Ti is commonly regarded as an immobile element, data from this study suggests the possibility of at least limited mobility of this element. The continued loss of P mass is nominal and likely the result of minor leaching of apatite.
