Batch Model with Brine Injection and Secondary Minerals Precipitation

I am attempting to set up a batch reaction model. Initially, the formation water equilibrates with calcite, gypsum, albite, illite, and k-feldspar. Then, I add a second water (brine) and allow it to equilibrate with the initial minerals, permitting potential secondary minerals to precipitate.

I am wondering about the best method to accomplish this in a single simulation. I am trying to use Problem1-BlackSea-evap-eos1, but instead of using water, I am injecting brine. I am uncertain about how to set up potential secondary minerals. Should I define the boundary conditions of water with the composition of brine and list all potential minerals that could precipitate as equilibrium minerals?

Thanks

Ben