The $ 1.2 billion is one of several revolving credit facilities available to Teck. When they lost their investment grade rating they were required to post letters of credit as required under existing contracts. In effect they had to post more collateral. They hope that they never have to use them. This has nothing to do with SC. Here's some extracts from the Q3 report:

At September 30, 2015, we had two undrawn committed revolving credit facilities in the amounts of US$3.0 billion and US$1.2 billion. The facility for US$1.2 billion is available until June 2017 and can be drawn fully for cash or letters of credit.

As a result of the loss of our investment grade rating in the third quarter, we are required to deliver an aggregate of US$672 million of letters of credit in the fourth quarter relating to financial security requirements under power purchase contracts for our Quebrada Blanca Operations. These letters of credit would be terminated if and when we regain investment grade ratings.

Our cash balance of $1.8 billion as of October 21 is more than our $1.5 billion share of costs required to complete Fort Hills. We also have an additional US$3 billion undrawn credit facility that can be used for general corporate purposes and US$1.2 billion available for cash draws or for letters of credit. We have certain contractual arrangements that may result in us having to issue letters of credit that would utilize substantially all of this US$1.2 billion facility.