The movement of fluids up reef lines is one of the hardest things to get ones head around and for years I tried to visualise an open crack or fissure being filled with reef forming material.
More recently the development of the orogenic model which involves the repeated opening and sealing of those cracks and fissures due to seismic activity over eons of time has made me more comfortable.
Under this model rock derived from seabed sediments containing raised levels of heavy elements such as gold is subducted under continental crusts by tectonic forces. At a great depth of around 15 - 20 Kms these rocks are "cooked" by the heat at that depth to mobilise large quantities of their water content which was previously contained either as free water in voids or bound chemically in minerals.
Due to the heat and pressure at that depth, this water, superheated to around 400 degrees is able to "scavenge" or dissolve and retain many elements from the heated plastic but not molten rocks it saturates.
This reservoir of hot fluid is normally kept in place by the overlaying layers of hardened, impervious and cooler rocks above.
During earthquakes, however, these rocks can be cracked which allows a conduit for the hot mineral rich water to escape the depths and under immense pressure be forced up the fault zones and cracks so formed.
As this fluid ascends its temperature, and pressure falls and it becomes unable to hold all of its dissolved minerals and some will deposit out. As the fluids ascend even higher progressive temperature and pressure drops enable more deposition over great lengths of the crack until the fluid is depleted of much of its mineral content. Current thinking puts this deposition zone for quartz and gold between 15Km to 3Km.
It is tempting to think of these cracks as open channels into which fluids flow upwards for long periods, but it is more probable that they are quite narrow and easily blocked by deposited quartz with closure further facilitated when the pressure of the escaping fluid drops and it is unable to counteract inward sidewall pressure.
A single crack/seal event is not likely to provide a great deal of reef material, but unstable tectonic periods can be long lasting, perhaps many millions of years in extent, during which hundreds if not thousands of earthquakes will occur. Each earthquake can reopen previously quartz sealed cracks and allow a fresh pulse of mineral and quartz rich fluid often along one wall of the crack allowing more deposition before resealing. Over many such crack/seal events reefs of considerable extent can build up.
The best evidence we have for these is the laminated quartz common in Victorian reefs where each lamination would appear to be evidence of a separate crack/seal event. Some samples show evidence at the microscopic scale of thousands of such laminations.
The subject is a complex one involving many variables but at least with a coherent model of orogenic reef formations, details such as the role of piezo electrostatic effects can start to be put in place.