Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_52 ( year_opened INTEGER, main_span_feet VARCHAR, country VARCHAR )

### Question ###
What is the oldest year with a main span feet of 1,640 in South Korea?

### Accurate SQL ###

SELECT MIN(year_opened) FROM table_name_52 WHERE main_span_feet = "1,640" AND country = "south korea"