Since your use case is spatial search, I don't think Cassandra's secondary index feature will work for you. Here's a fairly concise article on secondary indexes that you may find useful: http://www.datastax.com/docs/1.1/ddl/indexes
You should be able to do this with Solr.
Here's a post that should be relevant for you:
http://digbigdata.com/geospatial-search-cassandra-datastax-enterprise/