It didn't take long for us to decide that we'd do a second dive...A push to the bottom of the main shaft.  From the little information we had, the bottom appeared to be at ~175-200’, with a 3rd horizontal passage at the bottom.  However, in the days following our first dive, Matt did some research and gained an enormous amount of information for us, including maps.  Though the maps were old (the mine flooded somewhere around the 1930's) and hand drawn, we were able to ascertain that the bottom of the mine was probably either at ~200' or 120'.  We'd plan our dive based on 200' and would adjust as necessary.

For the dive, we'd use 18/45 in double 119's for backgas, with EAN50 and O2 for deco.  We'd run the profile on gas, instead of bottom time.  Since we had no idea what max depth was, if there'd be another passage, and if there was, how long it was.  

This, to me, is the beauty of ratio deco.  We enter the water with no deco tables, no computer (just a bottom timer), do our dive, and when the dive is over, we figure out our deco.  We can base our dive on gas, bottom time, or max deco time and adjust from there.  So, we'd do the dive.  Then, when the dive was over, we'd figure out our deco.  On 18/45, at 210', we'd have slightly more than 2 minutes of deco for every one minute on the bottom.  We do our deco on average depth, but if the passage was at the bottom, our average depth would probably be around 210'.

We descended.  The upper 20' is a very tight squeeze, then, the shaft opens quite nicely.  I tied off to the planned spot, while Jeanna video'd the main shaft.  We then continued down the shaft.  What's hard to see in the video is the shaft is very steep, almost vertical in some places.  At ~100' I arrived at a vertical ledge.  Looking over the ledge, it was pitch black.  It appeared as though we'd be making a vertical descent to 200' or so, as there was no bottom in sight.  I dropped down, and at about 112' I saw a glimmer below me.  At ~113-114' it became apparent that I was getting close to the bottom.  The bottom was at 115', and was the blackest silt I've ever seen.  That explained why Richard couldn't see the bottom on the first dive.  That also meant that the bottom of the mine was closer to the 120' that we thought was a possibility.  I tied off and looked around.  It was a fairly large room at the bottom.  To the west was a passage.  My initial thought was "sweet, we're only at 115' and a passage, PLENTY of time to explore”.  I led us into the passage, which opened into a smaller room that served as a Y.  To the south there was a passage that was about 40' long.  To the north, a 15' passage.  We explored both, then exited and started our ascent.

First, we saw another passage at about 53' on our descent.  We would explore that on our ascent.  Since we weren't sure how long it was, or how long it would take to explore, we might as well do that on deco, instead of backgas.

Second, on that profile, our slow tissues weren't a concern.  We'd switch to EAN50 at 70', stay there for 3 minutes , open the oxygen window and clean up our fast tissues.  Chances are we'd spend more time on EAN50 than required while exploring the 53' passage, so there'd be no need for O2.

The 53' passage was really cool.  It had several artifacts in it, including wooden crates that still had writing on them.  It was beyond a very tight restriction, but was about 25' in length with a bubble dome at the top of the very end.  We exited the passage and Richard signaled 1's up.  We stopped at 20', picked up our O2 bottles, and ascended single file through the tight upper portion.