I'd greatly appreciate any help with this insurance-related math question:

I have the average and the standard deviation of a set of claims ranging between $5,000 and $100,000. My data has no claims in it with values under $5,000 nor does it have any claims in it with values in excess of $100,000. If I'm willing to assume that the overall claim distribution is lognormal, how can I use the average and standard deviation for this limited set of data to derive the mu and sigma for the entire distribution?

Thanks in advance for any and all help!

- Steve J