Quartz deposition in a fracture

In our calculation, we need not be concerned with the dimensions of the fracture or the velocity of the fluid. Instead, we need specify only the length of time At it takes the fluid to travel from high-temperature conditions at depth to cool surface conditions. 

To model the problem, we take a packet of water in contact with the fracture walls over a polythermal reaction path. The fact that the packet moves relative to the walls is of no concern, since the fracture surface area exposed to the packet is approximately constant. Since the system contains 1 kg of water, we can show from geometry that the surface area 4s (in cm2) of the fracture lining is, 

i// is the surface roughness (surface area per unit area in cross section) of the fracture walls, p is fluid density in g cm-3, and the aperture 8 is taken in cm. For our purposes, it is sufficiently accurate to choose a value of 2 for 1// and set p to 1 g cm-3. In a fracture with an aperture of 10 cm, for example, each kg of water is exposed to 400 cm2 of quartz surface. 

To assign the amount of quartz in the system, we arbitrarily specify a specific surface area of 1 cm2 g-1. Then, we need only set the quartz mass to a value in grams equal to the desired surface area in cm2. Finally, we set for each run the amount of time At it takes the packet of water to flow along the fracture. 

To model the effects of flow through a 10 cm-wide fracture, assuming a time span of one year, for example, the procedure in REACT is 

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Quartz deposition in a fracture 26.2 Quartz deposition in a fracture... 

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