Geochemistry

Lecture 1: Equilibrium chemical alteration.  The simplest kind of chemical alteration occurs when fluids move through P,T, and/or [Cl] gradients while in equilibrium with their host rock.  How alteration of this kind can be computed is explained and illustrated in this workshop presentation.

Lecture 2: Computing patterns of oxygen isotope alteration.  The largest chemical constituent of water is oxygen, and the movement of water through P-T space produces a characteristic pattern of whole rock oxygen isotopic alteration.  How 18O alteration can be computed is explained and illustrated with detailed field studies at Noranda and elsewhere.

Lecture 3: Early biotite alteration in porphyry copper systems such as Butte resulted from diffusion of K from fractures into the host.  At first this formed vein halos.  When the halos merged the rock was completely biotized.  The biotized volume measures the total fluid vented, the width of the transition from completely altered to completely unaltered measures the flow rate.  Division gives the duration of the biotization event.  Butte was biotized (and heated to magmatic temperatures) in ~1000 years.  Copper mineralization occurred during retrograde cooling.

Lecture 4: Iron Oxide Copper Gold (IOCG) deposits seem to have resulted when CO2 escaped from the sub-continental mantle lithosphere (SCML).  The CO2-rich volatiles were magma pathfinders because they were not constrained by freezing.

Lecture 5: A new class of innocuous, inert, nano-particle can trace the actual pathways of fracture fluid flow by avoiding or greatly reducing diffusion into the host.  How tracers with varying diffusion constants and adsorption coefficients could characterize flow tens of meters from a well is described in a Cornell-CSU proto-proposal.

Lecture 6:  Oil matures and migrates first.  With further burial gas matures and migrates, interacting with the oil and removing “washing out” its smaller n- alkane content.  There is a remarkably regular pattern of “washing” over a distance of ~200 km in the offshore Louisiana Gulf of Mexico that measures the gas leakage and reveals the depth of gas-oil interaction.