Springs and saline lakes of the Sierra Nevada

We choose as a first example the evaporation of spring water from the Sierra Nevada mountains of California and Nevada, USA, as modeled by Garrels and Mackenzie (1967). Their hand calculation, the first reaction path traced in geochemistry (see Chapter 1), provided the inspiration for Helgeson s (1968 and later) development of computerized methods for reaction modeling. 

Garrels and Mackenzie wanted to test whether simple evaporation of groundwater discharging from the mountains, which is the product of the reaction of rainwater and CO2 with igneous rocks, could produce the water compositions found in the saline alkaline lakes of the adjacent California desert. They began with the mean of 

They made several assumptions about which minerals could precipitate from the fluid. The alkaline lakes tend to be supersaturated with respect to each of the silica polymorphs (quartz, tridymite, and so on) except amorphous silica, so they suppressed each of the other silica minerals. They assumed that 

The procedure to suppress these minerals and adjust the fluid s CO2 fugacity is 

The resulting fluid, which provides the starting point for modeling the effects of evaporation, has a pH of 8.2. 

Garrels and Mackenzie wanted to test whether simple evaporation of groundwater discharging from the mountains, which is the product of the 

TABLE 18.1 Mean composition of spring water from the Sierra Nevada, California and Nevada, USA (Garrels and Mackenzie, 1967) 

They made several assumptions about which minerals could precipitate from the fluid. The alkaline lakes tend to be supersaturated with respect to each of the 

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