hello everyone, my name is Gilbert and I am new to this forum, I have been using metal detectors for the past 15 yrs, my passion is cache hunting, all of which I do in south america.? I have not had enough time lately to do but only a little hunting since I am finishing my surgery training here in TN, but come July 06 I will head back down to do some serious searching.
I have not reviewed all the threads, but here are my two cents:
caches acumulate gas with time, wich is released during dry season when the ground has cracks in it, if this is out in the open , you will see a light blueish in the middle with white in the outside, this is the way that natives in South america find them, they stay up in august (winter) and wait at night where they suspect or someone has reported seeing before, this is also timed with the moon cycle as it affects this in a similar way as waves in the ocean.
old caches were hidden many times under or around brick ovens, or in old kitchen rooms, since the previous generations were aware that they will let off gas (that oxidizes with oxygen to give off light) so that if any one happened to see it they would think someone was cooking or baking.
if a cache is near? a rock or under a large rock, with time it will mark the rock, similar to the mark left behing by a candle if you let it burn agains a solid surface, the middle is light blue and outside black, and cannot be scratched off,(caused by gases that escape periodically) if you ever get to see that you will not forget it and will not need to turn on your detector if you ever encounter this again, at that point all you will need is digging equipment.
refering to the cave thread, make sure you have gas masks prior to digging inside a cave, and always have a dog with you, since they will detect the gas way before you will, even with all that care digging in a cave would be last on my list.? Try putting away a few silver coins in a ziplock bag with a wet paper towel, and open it a few months later, very peculiar smell, almost nauseating, someone mentioned to me that a component of oxidation is silver cyanide, but not sure only now of people having serios complications including death, that includes my great uncle.
if looking for deep treasure remember that once you dig a large hole, your detectors dont perform the same, so prior to start digging , measure lenghts with intensity of signal ( in all metal mode ) start when it is at max and stop when that signal starts to drop, repeat that in two directions, and also give your self a limit of how far you are willing to dig, because once you dig a deep hole your detector may not help to verify and you will be tempted to leave the job half way done.
if your loop detector detects something that seems good and large, verify with a two box, if the two box does not scream, then you are dealing with something small and superficial or mineral, now the oposite maneuver can be promising, however despite what reports and websites say , the detection? depth for a gallon size object is about the same between a two box and a loop detector that is used well, yes sounds weird but I have proven it over and over again, but I find a proper use for both.
Count on half the depth penetration of a detector for gold contents compared to say....copper alloys.
as for the previously dug areas, you can not tell by how soft the dirt is , it can be soft or hard.? pay more attention to the layers and how they have been interrupted with different color chunks in the wrong place or layers of rocks that dont match the sorroundings
most personal caches average of 50 cm deep, Inca treasures about 4 meters + deep
I am a little tired and have to go to the work early, hope this was of some interest, I will add some more experiences some other time
Gilbert
The best for shooting paint on cars is good.
Do Not! Allow ANYONE! to rely on a gas mask! ![:-\](https://www.treasurenet.com/smilies/undecided.gif "Undecided :-\")
AND! You get to pick the one that has/hasnt ! 
...they were out the door 
AND! Don't light a match to find out! 
