Question
I have a pond about 60'x60' x 13 ft deep.
it is lined and in a oak forest. many frogs die and line the shore late winter early
spring my wife cries and i need to figure out the deaths. Is the ph from the oak
leaves too much. the pond freezes over for weeks at a time,m thick ice, not
practical to keep breaking ice to let it breath

Answer
That's a big pond!

My biggest pond is only 1800 gallons but I too lose some frogs each year.  Frogs die over the winter from two major problems.  The first is lack of oxygen.  While hibernating under the water, they need all their oxygen from the water.  In ponds that are frozen over and/or deep like yours, the oxygen levels may fall too low to sustain life on the bottom.  It's not practical for you to have a de-icer as it would do little in such a large pond.  I do, however, suggest an aerator.  Aerators can be run in larger ponds all year.  They move water and aerate the water.  This can safe not only many frogs but also fish that may suffer from low oxygen.

One way to help the frogs might be to have an area that is only two or three feet deep.  That should be deep enough that it doesn't freeze solid but not so deep that the oxygen is really low.  Even in the summer, oxygen levels are low in the bottom of a 13 foot deep pond.  I don't know if your pond is all that deep or just parts of it.

The other problem that hits frogs in the winter is fungus.  The fungus keeps growing when it's cold and the frogs are weak.  There's not really anything you can do about that.  

My page on overwintering frogs is at http://www.fishpondinfo.com/frog3.htm

My winterizing page in general is at http://www.fishpondinfo.com/winter.htm

My page on larger ponds like yours including links to companies that sell the larger aerators like you might need is at http://www.fishpondinfo.com/farm.htm

Good luck!