AboutKeith Patton Expertise I can answer questions concerning physical and historical geology, environmental geology/hydrology, environmental consulting, remote sensing/aerial photo interpretation, G&G computer applications, petroleum exploration, drilling, geochemistry, geochemical and microbiological prospecting, 3D reservoir modeling, computer mapping and drilling.I am not a geophysicist.
Experience I have 24 years experience split between the petroleum and environmental industries. I have served as an expert witness in remote sensing, developmental geologist, exploration geologist, enviromental project manager, and subject matter expert in geology and geophysical software development.
Organizations American Association of Petroleum Geologists
American Association of Photogrammetrists and Remote Sensing
Education/Credentials Bachelor and Master of Science
Registered Geologist in State of Texas
Question QUESTION: "The locals that lived around my father's property collected water from the spring from centuries ago. We belive the water comes from a mountain that has been studied and findings were that the mountain is full of water, sulfur and gold. The spring is about a 12ft by 12ft circular in shape hole. It drains about 75ft away from the spring into a small hole in the ground. It's been this way always. We think there must be a gigantic cave under our house and would like to explore what can be found in this cave. Could we be right? Who can help us and how?
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ANSWER: Marlene:
Springs come in several types. An artesian spring is one that bubbles up under a substantial amount of pressure. These occur when an aquifer is confined by an upper and lower layer resulting in water moving in a constricted layer. Water in the form of precipitation comes down in a recharge area either rain or melt water from snow. and infiltrates down through porous rock or fractures into the aquifer. The water follows the acquifer down gradient (down hill) and if it becomes constricted, develops what we call "hydraulic head" This is the amount of pressure that results from the differenct in elevation between where the water is first confined and the outlet.
You can demonstrate this with a piece of tube or hose. Fill it with water and hold one end at a constant level, then raise the other a bit above that level and some water will flow out the lower end. Okay now quickly raise one end as high as you can above your head. The water no longer just flows out, it now fountains out more quickly, because you have created more hydraulic head by increasing the difference in elevation.
Right. So that is what an artesian spring is.
Other "Springs" are merely the intersection of a flowing body of subsurface water with the surface. In Virginia's Shenendoah Valley where I am from, the area is underlain by limestone and is known to be underlain by caverns. Many people own property that had spring houses built over "springs" to protect them and to afford the owners with fresh flowing water during all seasons. The springs occurred near creeks and streams and were really only the intersection of an underground stream flowing though the porous limestone and the downward cutting banks of the surface creek. Many residents report the sound of running water beneath their houses during periods of rain. Their homes sit atop other underground streams whose outlets into the nearby creeks occur out of sight, probably deeper along the banks where they are not visible.
This is call discharge and is why creeks and rivers continue to run full of water even when there has not been any rain.
So from your description I think you have one of the latter types. You do not say where it is or what the rock composition of the mountain is, but it sounds like you have groundwater moving through fractures and possibly caverns in limestone. This flow comes to the surface for one reason or another at the location of your spring, then resumes its subteranean passage when it disappears into the adjoining hole farther down gradient.
The cave does not have to be gigantic. These types of caverns only occur in limestone rock, a rock that is suseptible to solutioning or dissolving in water over long periods to time.
If you are not in an area underlain by limestone, it could merely be a result of highly fractured rock of another type associated with faulting related to the formation of the mountain.
I would get a geological quadrangle map of your area, a 1:24000 scale if available from your state geological survey. This has a scale of about 2.5 inches to the mile and should have enought detail to see the faults and the type of rock underlying the area in which you live.
They might even have a special publication covering springs or the area of the mountain if it was considered of enough geological interest to warrant a detailed investigation in the past by some curious state geologist. This kind of publcication would give you more information than you could use but would explain most everything to you.
As far as your own investigation, there are several types of non-invasive procedures that could help you map your cavern. One is a manual seismographic device that sends sound waves into the shallow subsurface and will map voids. Ground penetrating radar will do the same thing.
http://www.geometrics.com/ Provides rentals. An email to them and they could set you up with what you need minimally to do the job.
They rent too and their profiler would work. You simply walk along a grid lines you have mapped out on your property and the hand held antenae transmits radar energy into the ground and void will cleary show up on the hand held screen. You could then dump the data logger to your computer and prepare a map view, what we call a fence diagram of the intersecting line profiles. then it is simply connect the dots so to speak to generate a plan view or map of the area.
Opening the cave is another thing entirely. Depending on the rock type the mountain is composed of and the geologic history, gold may not have formed in the area. Gold most certainly is not found in karst or limestone areas. Usually only in areas of granite that has undergone hydrothermal enrichment...which is depostion by superheated water coming from large magma source deep in the earth and precipitated out in fractures inside the granite body.
Keith
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QUESTION: Thank you for all the information. We belive the rock is geo-hydrothermal rock, since the island is on a dormant volcano in the Caribbean. I would appreciate more advice if possible.
Answer Marlene:
To be geothermal implies the water is hot. If it is not, then it is not geothermal and all the stuff I said above applies.
Volcanoes form below the surface and reefs grow on the shoulders forming the characteristic lagoon and reef structure. If your volcanic island formed reefs at a time when sea level was higher, then limestone would be found pretty much all over the exposed surface, underlain by volcanic basalts. Basalt is a dark very dense rock, the limestone is porous, gray to white.
It is prone to dissolution like I described above when subaerially exposed, or in other words, when it is raised above the sea level where it can now be exposed to fresh water its affects and starts to form karst topography.
Based on what I have heard, I think my explaination of the subterranean stream coming up and then going back down is closest to the truth.
If the water is hot, and comes to the surface and cools even a little bit, you should see lots of depostion of lime or other minerals that precipitate out as the dissolved minerals are deposited. This is because the cooler water cannot carry all the dissolve minerals that it could when it was much hotter. Just like how you can dissolve more sugar or salt in water on the stove when you heat it than you can when it it cold.
