if you can be specific in which area you want to explore.
Text mining is a vast domain, which I feel can be divided in broadly three areas indexing/ searching, entity extraction, and relation extraction or natural language processing.
you can check literature on Latent Semantic Analysis, if you are interested in understanding how document analysis is done or Conditional Random Fields if you are interested in understanding how entity extraction is done. Even NLP has vast documentation available online. Please explore and let me know if you need any help in any particular area.