Missing wife

My great grandfather John McCully Cairns, born & died Belfast 1851- 1901 had three wives. Wife 2: Mary Ann Russell 1851-1889, married 13 April, 1875 at College Square Presbyterian Church, Belfast is my great grandmother. After her death he married Margaret Ann Patchell, born 4 April 1871 in Londonderry, married June, 1890. However I believe John had a wife prior to Mary Ann but cannot find any details - although she would have no direct link to me, any children would have been half brother/sister to my grandfather [ John Kennedy Cairns, born Belfast, 28 July 1880, died Australia 26 December, 1942 ] and may have been the reason my grandfather immigrated to Australia in 1911. Any help with this would be appreciated.