Explanation/Reference:
To create a partitioned spatial index, you must specify the LOCAL keyword. (If you do not specify the LOCAL keyword, a nonpartitioned spatial index is created on the data in all table partitions.) The following example creates a partitioned spatial index:
CREATE INDEX counties_idx ON counties(geometry)
INDEXTYPE IS MDSYS.SPATIAL_INDEX LOCAL;
Note: The following restrictions apply to spatial index partitioning:
The partition key for spatial tables must be a scalar value, and must not be a spatial column.

Only range partitioning is supported on the underlying table. All other kinds of partitioning are not

currently supported for partitioned spatial indexes.
References: https://docs.oracle.com/cd/B28359_01/appdev.111/b28400/sdo_index_query.htm#SPATL586