How can I mount partition disk0s4 that became inaccessible after a clean installation of Mountain Lion?

$ diskutil list disk12
/dev/disk12
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *256.9 MB   disk12
   1:                  Apple_UFS sandpit                 256.9 MB   disk12s1
$ diskutil mount readOnly /dev/disk12s1
Volume on disk12s1 failed to mount
$ sudo asr adjust --target /dev/disk12s1 --settype "Apple_HFS"
Fsck /dev/disk12s1 ....10....20....30....40....50....60....70....80....90....100
Adjust completed successfully

http://apple.stackexchange.com/questions/59118/how-can-i-mount-partition-disk0s4-that-became-inaccessible-after-a-clean-install

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